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_basic/Android.bp b/opengl/tests/gl2_basic/Android.bp
index 7403271..f4538ad 100644
--- a/opengl/tests/gl2_basic/Android.bp
+++ b/opengl/tests/gl2_basic/Android.bp
@@ -16,5 +16,10 @@
 
     static_libs: ["libglTest"],
 
-    cflags: ["-DGL_GLEXT_PROTOTYPES"],
+    cflags: [
+        "-DGL_GLEXT_PROTOTYPES",
+        "-Wall",
+        "-Werror",
+    ],
+
 }