LibC: Remove duplicate declaration of clock_t and time_t

These are pulled from Kernel/API/POSIX/sys/types.h. Removing these
declarations makes sure we only have one place defining them.

Userland/Libraries/LibC/time.h

@@ -28,9 +28,6 @@ extern long altzone;
 extern char* tzname[2];
 extern int daylight;
 
-typedef uint32_t clock_t;
-typedef int64_t time_t;
-
 struct tm* localtime(time_t const*);
 struct tm* gmtime(time_t const*);
 time_t mktime(struct tm*);