Remove g:python{,3}_host_skip_check (#5738)

This option simplifies the configuration options:

1) `g:python{,3}_host_prog` is not set.

    Neovim tries its best to find a suitable interpreter. This means calling
    exepath(), potentially multiple times, and a system('python -c ...') with
    the first found interpreter, to get the Python version.

2) `g:python{,3}_host_prog` is set.

    Avoids everything of the above. No safety checks, no training wheels. Fast
    host startup time!

runtime/autoload/health/provider.vim

@@ -215,7 +215,6 @@ function! s:check_python(version) abort
   let pyenv_root = exists('$PYENV_ROOT') ? resolve($PYENV_ROOT) : 'n'
   let venv = exists('$VIRTUAL_ENV') ? resolve($VIRTUAL_ENV) : ''
   let host_prog_var = python_bin_name.'_host_prog'
-  let host_skip_var = python_bin_name.'_host_skip_check'
   let python_bin = ''
   let python_multiple = []
 
@@ -230,10 +229,6 @@ function! s:check_python(version) abort
     if !empty(pythonx_errs)
       call health#report_warn(pythonx_errs)
     endif
-    let old_skip = get(g:, host_skip_var, 0)
-    let g:[host_skip_var] = 1
-    let [python_bin_name, pythonx_errs] = provider#pythonx#Detect(a:version)
-    let g:[host_skip_var] = old_skip
   endif
 
   if !empty(python_bin_name)

runtime/autoload/provider/pythonx.vim

@@ -47,32 +47,27 @@ function! provider#pythonx#Require(host) abort
 endfunction
 
 function! provider#pythonx#Detect(major_ver) abort
-  let host_var = (a:major_ver == 2) ?
-        \ 'g:python_host_prog' : 'g:python3_host_prog'
-  let skip_var = (a:major_ver == 2) ?
-        \ 'g:python_host_skip_check' : 'g:python3_host_skip_check'
-  let skip = exists(skip_var) ? {skip_var} : 0
-  if exists(host_var)
-    " Disable auto detection.
-    let [result, err] = s:check_interpreter({host_var}, a:major_ver, skip)
-    if result
-      return [{host_var}, err]
+  if a:major_ver == 2
+    if exists('g:python_host_prog')
+      return [g:python_host_prog, '']
+    else
+      let progs = ['python2', 'python2.7', 'python2.6', 'python']
+    endif
+  else
+    if exists('g:python3_host_prog')
+      return [g:python3_host_prog, '']
+    else
+      let progs = ['python3', 'python3.5', 'python3.4', 'python3.3', 'python']
     endif
-    return ['', 'provider/pythonx: Could not load Python ' . a:major_ver
-          \ . ' from ' . host_var . ': ' . err]
   endif
 
-  let prog_suffixes = (a:major_ver == 2) ?
-        \   ['2', '2.7', '2.6', '']
-        \ : ['3', '3.5', '3.4', '3.3', '']
-
   let errors = []
-  for prog in map(prog_suffixes, "'python' . v:val")
-    let [result, err] = s:check_interpreter(prog, a:major_ver, skip)
+
+  for prog in progs
+    let [result, err] = s:check_interpreter(prog, a:major_ver)
     if result
       return [prog, err]
     endif
-
     " Accumulate errors in case we don't find
     " any suitable Python interpreter.
     call add(errors, err)
@@ -83,16 +78,12 @@ function! provider#pythonx#Detect(major_ver) abort
         \ . ":\n" .  join(errors, "\n")]
 endfunction
 
-function! s:check_interpreter(prog, major_ver, skip) abort
+function! s:check_interpreter(prog, major_ver) abort
   let prog_path = exepath(a:prog)
   if prog_path ==# ''
     return [0, a:prog . ' not found in search path or not executable.']
   endif
 
-  if a:skip
-    return [1, '']
-  endif
-
   let min_version = (a:major_ver == 2) ? '2.6' : '3.3'
 
   " Try to load neovim module, and output Python version.

runtime/doc/provider.txt

@@ -48,11 +48,9 @@ Note: The `--upgrade` flag ensures you have the latest version even if
 
 PYTHON PROVIDER CONFIGURATION ~
 						*g:python_host_prog*
-Set `g:python_host_prog` to point Nvim to a specific Python 2 interpreter: >
-    let g:python_host_prog = '/path/to/python'
-<
 						*g:python3_host_prog*
-Set `g:python3_host_prog` to point Nvim to a specific Python 3 interpreter: >
+Program to use for evaluating Python code. Setting this makes startup faster. >
+    let g:python_host_prog  = '/path/to/python'
     let g:python3_host_prog = '/path/to/python3'
 <
 						*g:loaded_python_provider*
@@ -62,16 +60,6 @@ To disable Python 2 support: >
 						*g:loaded_python3_provider*
 To disable Python 3 support: >
     let g:loaded_python3_provider = 1
-<
-						*g:python_host_skip_check*
-Set `g:python_host_skip_check` to disable the Python 2 interpreter check.
-Note: This requires you to install the python-neovim module properly. >
-    let g:python_host_skip_check = 1
-<
-						*g:python3_host_skip_check*
-Set `g:python3_host_skip_check` to disable the Python 3 interpreter check.
-Note: This requires you to install the python3-neovim module properly. >
-    let g:python3_host_skip_check = 1
 
 
 ==============================================================================