vim-patch.sh: Remove "set -o pipefail"

grep 2.26 changed its behavior when redirecting its output to /dev/null
such that it exits as soon as one match is found.  This causes sed to
get a SIGPIPE which, due to "set -o pipefail", falsely implies that the
patch is not applied.

Removing "set -o pipefail" preserves the good exit status from grep.

scripts/vim-patch.sh

@@ -2,7 +2,6 @@
 
 set -e
 set -u
-set -o pipefail
 # Use privileged mode, which e.g. skips using CDPATH.
 set -p