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)
 {

prune-packed.c

@@ -1,6 +1,6 @@
 #include "cache.h"
 
-static const char prune_packed_usage[] = "git-prune-packed: usage: git-prune-packed";
+static const char prune_packed_usage[] = "git-prune-packed (no arguments)";
 
 static void prune_dir(int i, DIR *dir, char *pathname, int len)
 {

rev-list.c

@@ -11,7 +11,7 @@
 #define SHOWN		(1u << 3)
 
 static const char rev_list_usage[] =
-	"usage: git-rev-list [OPTION] commit-id <commit-id>\n"
+	"git-rev-list [OPTION] commit-id <commit-id>\n"
 		      "  --max-count=nr\n"
 		      "  --max-age=epoch\n"
 		      "  --min-age=epoch\n"