Removed support for clock_gettime_nsec_np()

SDL_GetTicks() was broken and it's not adding any real value here.

CMakeLists.txt

@@ -875,18 +875,6 @@ if(LIBC)
     else()
       set(HAVE_ALLOCA_H 1)
       set(HAVE_ALLOCA 1)
-      if(IOS OR TVOS)   # assuming iOS / TVOS >= 10.0
-        set(HAVE_CLOCK_GETTIME_NSEC_NP 1)
-      else()
-        CHECK_C_SOURCE_COMPILES("
-          #include <AvailabilityMacros.h>
-          #include <time.h>
-          #if MAC_OS_X_VERSION_MIN_REQUIRED < 101200
-          #error Need 10.12 or newer target
-          #endif
-          int main(int argc, char **argv) { return !clock_gettime_nsec_np(CLOCK_MONOTONIC); }
-        " HAVE_CLOCK_GETTIME_NSEC_NP)
-      endif()
     endif()
 
     check_struct_has_member("struct sigaction" "sa_sigaction" "signal.h" HAVE_SA_SIGACTION)