Use -Werror in frameworks/native/opengl/tests

* Remove or comment out unused local variables.
* Remove unused function.
* Cast print argument type to fix format mismatch warning.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I81e80849ac36288932df235cb0d63bd870357d86
diff --git a/opengl/tests/gl2_yuvtex/Android.bp b/opengl/tests/gl2_yuvtex/Android.bp
index 613d678..b64d94d 100644
--- a/opengl/tests/gl2_yuvtex/Android.bp
+++ b/opengl/tests/gl2_yuvtex/Android.bp
@@ -20,5 +20,7 @@
     cflags: [
         "-DGL_GLEXT_PROTOTYPES",
         "-DEGL_EGLEXT_PROTOTYPES",
+        "-Wall",
+        "-Werror",
     ],
 }