emulator: opengl: Add clean step.

The previous changes replaced /system/lib/libGLES_emul.so with
several other libraries (lib{EGL, GLESv1_CM, GLESv2}_emul.so).

The clean step removes the old libGLES_emul.so from the build to
avoid any surprises.

Change-Id: I285b34c4d5f5a8bd3b37d9cb1b2da33fb155e62c
1 file changed