prefixcmp(): fix-up mechanical conversion.

Previous step converted use of strncmp() with literal string
mechanically even when the result is only used as a boolean:

    if (!strncmp("foo", arg, 3)) ==> if (!(-prefixcmp(arg, "foo")))

This step manually cleans them up to read:

    if (!prefixcmp(arg, "foo"))

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/builtin-tar-tree.c b/builtin-tar-tree.c
index 28f8c1c..b04719e 100644
--- a/builtin-tar-tree.c
+++ b/builtin-tar-tree.c
@@ -31,7 +31,7 @@
 	nargv[nargc++] = "git-archive";
 	nargv[nargc++] = "--format=tar";
 
-	if (2 <= argc && !(-prefixcmp(argv[1], "--remote="))) {
+	if (2 <= argc && !prefixcmp(argv[1], "--remote=")) {
 		nargv[nargc++] = argv[1];
 		argv++;
 		argc--;