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/t7417-submodule-path-url.sh

@@ -21,7 +21,7 @@ test_expect_success 'create submodule with dash in path' '
 test_expect_success 'clone rejects unprotected dash' '
 	test_when_finished "rm -rf dst" &&
 	git clone --recurse-submodules . dst 2>err &&
-	test_i18ngrep ignoring err
+	test_grep ignoring err
 '
 
 test_expect_success 'fsck rejects unprotected dash' '
@@ -46,7 +46,7 @@ test_expect_success MINGW 'submodule paths disallows trailing spaces' '
 	git -C super update-ref refs/heads/main $commit &&
 
 	test_must_fail git clone --recurse-submodules super dst 2>err &&
-	test_i18ngrep "sub " err
+	test_grep "sub " err
 '
 
 test_done