meson: Remove obsolete function test

The test for pstat was removed from configure by 9db300c but not
from meson.build.  Do that now.

Author: petere

meson.build

@@ -2537,7 +2537,6 @@ func_checks = [
   ['posix_fadvise'],
   ['posix_fallocate'],
   ['ppoll'],
-  ['pstat'],
   ['pthread_barrier_wait', {'dependencies': [thread_dep]}],
   ['pthread_is_threaded_np', {'dependencies': [thread_dep]}],
   ['sem_init', {'dependencies': [rt_dep, thread_dep], 'skip': sema_kind != 'unnamed_posix', 'define': false}],