evas gl: remove unnecessary null check.

If we check reference validation, the rest of other usage
should keep the reference check as well.

Remove it since gl prorgram must be valid always here
to shutdown the static analyzer reporting this suspicous logic.

src/modules/evas/engines/gl_common/evas_gl_context.c

@@ -3769,8 +3769,7 @@ shader_array_flush(Evas_Engine_GL_Context *gc)
         pipe_done++;
         gc->flushnum++;
 
-        GLERRV("<flush err>");
-        if (prog && (prog != gc->state.current.prog))
+        if (prog != gc->state.current.prog)
           {
              glUseProgram(prog->prog);
              if (prog->reset)