Revert "Windows: teach getenv to do a case-sensitive search"

This reverts commit df599e9612.

As of 5e9637c6 "i18n: add infrastructure for translating Git with gettext",
eval_gettext uses MinGW envsubst.exe instead of git-sh-i18n--envsubst.exe
for variable substitution. This breaks git-submodule.sh messages and tests,
as envsubst.exe doesn't support case-sensitive environment lookup (the same
is true for almost everything on Windows, including MSys and Cygwin tools).

30a615ac "Windows/i18n: rename $path to prevent clashes with $PATH" renames
the conflicting variable in git-submodule.sh, so that it works on Windows
(i.e. with case-insensitive environment, regardless of the toolset).

Revert to the documented behaviour of case-insensitive environment on
Windows.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Stepan Kasal <kasal@ucw.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -1245,31 +1245,14 @@ char **make_augmented_environ(const char *const *vars)
 }
 
 #undef getenv
-
-/*
- * The system's getenv looks up the name in a case-insensitive manner.
- * This version tries a case-sensitive lookup and falls back to
- * case-insensitive if nothing was found.  This is necessary because,
- * as a prominent example, CMD sets 'Path', but not 'PATH'.
- * Warning: not thread-safe.
- */
-static char *getenv_cs(const char *name)
-{
-	size_t len = strlen(name);
-	int i = lookup_env(environ, name, len);
-	if (i >= 0)
-		return environ[i] + len + 1;	/* skip past name and '=' */
-	return getenv(name);
-}
-
 char *mingw_getenv(const char *name)
 {
-	char *result = getenv_cs(name);
+	char *result = getenv(name);
 	if (!result && !strcmp(name, "TMPDIR")) {
 		/* on Windows it is TMP and TEMP */
-		result = getenv_cs("TMP");
+		result = getenv("TMP");
 		if (!result)
-			result = getenv_cs("TEMP");
+			result = getenv("TEMP");
 	}
 	return result;
 }