Typofix: usage strings fix.

The *_usage strings should not start with "usage: ", since the
usage() function gives its own.

Signed-off-by: Junio C Hamano <junkio@cox.net>

patch-id.c

@@ -67,7 +67,7 @@ static void generate_id_list(void)
 	flush_current_id(patchlen, sha1, &ctx);
 }
 
-static const char patch_id_usage[] = "usage: git-patch-id < patch";
+static const char patch_id_usage[] = "git-patch-id < patch";
 
 int main(int argc, char **argv)
 {