tests: teach callers of test_i18ngrep to use test_grep

They are equivalents and the former still exists, so as long as the
only change this commit makes are to rewrite test_i18ngrep to
test_grep, there won't be any new bug, even if there still are
callers of test_i18ngrep remaining in the tree, or when merged to
other topics that add new uses of test_i18ngrep.

This patch was produced more or less with

    git grep -l -e 'test_i18ngrep ' 't/t[0-9][0-9][0-9][0-9]-*.sh' |
    xargs perl -p -i -e 's/test_i18ngrep /test_grep /'

and a good way to sanity check the result yourself is to run the
above in a checkout of c4603c1c (test framework: further deprecate
test_i18ngrep, 2023-10-31) and compare the resulting working tree
contents with the result of applying this patch to the same commit.
You'll see that test_i18ngrep in a few t/lib-*.sh files corrected,
in addition to the manual reproduction.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9815-git-p4-submit-fail.sh

@@ -35,7 +35,7 @@ test_expect_success 'conflict on one commit' '
 		git add file1 &&
 		git commit -m "line3 in file1 will conflict" &&
 		test_expect_code 1 git p4 submit >out &&
-		test_i18ngrep "No commits applied" out
+		test_grep "No commits applied" out
 	)
 '
 
@@ -58,7 +58,7 @@ test_expect_success 'conflict on second of two commits' '
 		git add file1 &&
 		git commit -m "line4 in file1 will conflict" &&
 		test_expect_code 1 git p4 submit >out &&
-		test_i18ngrep "Applied only the commits" out
+		test_grep "Applied only the commits" out
 	)
 '
 
@@ -81,7 +81,7 @@ test_expect_success 'conflict on first of two commits, skip' '
 		# but this commit is okay
 		test_commit "okay_commit_after_skip" &&
 		echo s | test_expect_code 1 git p4 submit >out &&
-		test_i18ngrep "Applied only the commits" out
+		test_grep "Applied only the commits" out
 	)
 '
 
@@ -104,7 +104,7 @@ test_expect_success 'conflict on first of two commits, quit' '
 		# but this commit is okay
 		test_commit "okay_commit_after_quit" &&
 		echo q | test_expect_code 1 git p4 submit >out &&
-		test_i18ngrep "No commits applied" out
+		test_grep "No commits applied" out
 	)
 '
 
@@ -144,7 +144,7 @@ test_expect_success 'conflict on first of two commits, --conflict=skip' '
 		# but this commit is okay
 		test_commit "okay_commit_after_auto_skip" &&
 		test_expect_code 1 git p4 submit --conflict=skip >out &&
-		test_i18ngrep "Applied only the commits" out
+		test_grep "Applied only the commits" out
 	)
 '
 
@@ -167,7 +167,7 @@ test_expect_success 'conflict on first of two commits, --conflict=quit' '
 		# but this commit is okay
 		test_commit "okay_commit_after_auto_quit" &&
 		test_expect_code 1 git p4 submit --conflict=quit >out &&
-		test_i18ngrep "No commits applied" out
+		test_grep "No commits applied" out
 	)
 '