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/testdisplay.c

@@ -504,7 +504,7 @@ static void stereo_fb_layout_from_mode(struct stereo_fb_layout *layout,
 		break;
 	}
 	default:
-		assert(0);
+		igt_assert(0);
 	}
 }
 
@@ -520,7 +520,7 @@ static const char *stereo_mode_str(drmModeModeInfo *mode)
 	case DRM_MODE_FLAG_3D_FRAME_PACKING:
 		return "FP";
 	default:
-		assert(0);
+		igt_assert(0);
 	}
 }