tests|lib: remove assert.h includes

Only the igt core and non-test tools should have asserts to catch
internal errors, tests and helper libraries should all user igt_asert
instead.

Fix things up where assert instead of igt_assert was used.

One tiny step towards header sanity.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

tests/gem_ctx_basic.c

@@ -30,12 +30,10 @@
  */
 
 #include <pthread.h>
-#include <assert.h>
 #include <stdlib.h>
 #include <sys/ioctl.h>
 #include <stdio.h>
 #include <string.h>
-#include <assert.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <errno.h>