Fixed testautomation --filter pixels_allocFreePalette

Error messages are not part of the ABI, so we can't validate those.

Hand-picked from https://github.com/libsdl-org/sdl2-compat/commit/c9323f8face982983668fca216a2eef12dc8b1f7

test/testautomation_pixels.c

@@ -294,7 +294,6 @@ int pixels_getPixelFormatName(void *arg)
 int pixels_allocFreePalette(void *arg)
 {
     const char *expectedError1 = "Parameter 'ncolors' is invalid";
-    const char *expectedError2 = "Parameter 'palette' is invalid";
     const char *error;
     int variation;
     int i;
@@ -359,19 +358,6 @@ int pixels_allocFreePalette(void *arg)
         }
     }
 
-    /* Invalid free pointer */
-    SDL_ClearError();
-    SDLTest_AssertPass("Call to SDL_ClearError()");
-    SDL_FreePalette(NULL);
-    SDLTest_AssertPass("Call to SDL_FreePalette(NULL)");
-    error = SDL_GetError();
-    SDLTest_AssertPass("Call to SDL_GetError()");
-    SDLTest_AssertCheck(error != NULL, "Validate that error message was not NULL");
-    if (error != NULL) {
-        SDLTest_AssertCheck(SDL_strcmp(error, expectedError2) == 0,
-                            "Validate error message, expected: '%s', got: '%s'", expectedError2, error);
-    }
-
     return TEST_COMPLETED;
 }