environment: normalize use of prefixcmp() by removing " != 0"

To be able to automatically convert prefixcmp() to starts_with()
we need first to make sure that prefixcmp() is always used in
the same way.

So let's remove " != 0" after prefixcmp().

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

environment.c

@@ -171,7 +171,7 @@ const char *get_git_namespace(void)
 
 const char *strip_namespace(const char *namespaced_ref)
 {
-	if (prefixcmp(namespaced_ref, get_git_namespace()) != 0)
+	if (prefixcmp(namespaced_ref, get_git_namespace()))
 		return NULL;
 	return namespaced_ref + namespace_len;
 }