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/textures/Android.mk b/opengl/tests/textures/Android.mk
index bee61f9..629a2d2 100644
--- a/opengl/tests/textures/Android.mk
+++ b/opengl/tests/textures/Android.mk
@@ -21,5 +21,6 @@
 LOCAL_MODULE_TAGS := optional
 
 LOCAL_CFLAGS := -DGL_GLEXT_PROTOTYPES
+LOCAL_CFLAGS += -Wall -Werror
 
 include $(BUILD_EXECUTABLE)