libc: Use time/getdate.c from upstream musl

The difference is minimal so switch to upstream musl:

[penberg@nero osv]$ diff -u libc/time/getdate.c musl/src/time/getdate.c
--- libc/time/getdate.c	2014-08-07 21:58:30.627818727 +0300
+++ musl/src/time/getdate.c	2014-08-07 22:04:44.906664048 +0300
@@ -6,8 +6,6 @@

 int getdate_err;

-char *strptime(const char *__restrict s, const char *__restrict f, struct tm *__restrict tm);
-
 struct tm *getdate(const char *s)
 {
 	static struct tm tmbuf;

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>