git-sh-setup: remove "sane_grep", it's not needed anymore

Remove the sane_grep() shell function in git-sh-setup. The two reasons
for why it existed don't apply anymore:

1. It was added due to GNU grep supporting GREP_OPTIONS. See
   e1622bfcba (Protect scripted Porcelains from GREP_OPTIONS insanity,
   2009-11-23).

   Newer versions of GNU grep ignore that, but even on older versions
   its existence won't matter, none of these sane_grep() uses care
   about grep's output, they're merely using it to check if a string
   exists in a file or stream. We also don't care about the "LC_ALL=C"
   that "sane_grep" was using, these greps for fixed or ASCII strings
   will behave the same under any locale.

2. The SANE_TEXT_GREP added in 71b401032b (sane_grep: pass "-a" if
   grep accepts it, 2016-03-08) isn't needed either, none of these grep
   uses deal with binary data.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-sh-setup.sh

@@ -173,10 +173,6 @@ git_pager() {
 	eval "$GIT_PAGER" '"$@"'
 }
 
-sane_grep () {
-	GREP_OPTIONS= LC_ALL=C grep @@SANE_TEXT_GREP@@ "$@"
-}
-
 is_bare_repository () {
 	git rev-parse --is-bare-repository
 }