MRTs: an attempt to fix crash issue when running with a real Android device.
MRTs: an attempt to fix crash issue when running with a real Android device.

I think the crash is due to a glDrawBuffers with 4 GL_BACKs. The call
will actually return GL_INVALID_OPERATION.
I removed this call as we are not rendering in the 2nd pass (we are just
copying buffers).

RainbowYou/opengles3-book,ryoenji/opengles3-book,micrologic/opengles3-book,weizhenwei/opengles3-book,lyntel/opengles3-book,weizhenwei/opengles3-book,galek/opengles3-book,galek/opengles3-book,leonhe/opengles3-book,gougoudetao/OpenglES,danginsburg/opengles3-book,ryoenji/opengles3-book,gougoudetao/OpenglES,micrologic/opengles3-book,RainbowYou/opengles3-book,Bvnkame/opengles3-book,zhakui/opengles3-book,danginsburg/opengles3-book,leonhe/opengles3-book,zhakui/opengles3-book,ryoenji/opengles3-book,Bvnkame/opengles3-book,weizhenwei/opengles3-book,danginsburg/opengles3-book,Bvnkame/opengles3-book,zhakui/opengles3-book,galek/opengles3-book,lyntel/opengles3-book,micrologic/opengles3-book,gougoudetao/OpenglES,RainbowYou/opengles3-book,leonhe/opengles3-book,lyntel/opengles3-book