The tests would leave the following test files in the root directory:
Xtest-functional-plugin-shada.shada
Xtest-functional-plugin-shada.shada.tmp.f
Clean them up in teardown().
Note: it looks like viminfo files do not store search direction intentionally.
After reading viminfo file search direction was considered to be “forward”.
Note 2: all files created on earlier Neovim version will automatically receive
“forward” direction.
Fixes#3580
