A future CL will add external frame buffers
differently.

Squash commit of four revert commits:
Revert "Increase required number of external frame buffers"

This reverts commit 9e41d569.

Revert "Add external constants."

This reverts commit bbf53047.

Revert "Add frame buffer lru cache."

This reverts commit fbada948.

Conflicts:
	vpxdec.c

Change-Id: I76fe42419923a6ea6c75d9997cbbf941d73d3005

Revert "Add support to pass in external frame buffers."

This reverts commit 10f89169.

Conflicts:
	test/external_frame_buffer_test.cc
	vp9/common/vp9_alloccommon.c
	vp9/common/vp9_reconinter.c
	vp9/decoder/vp9_decodeframe.c
	vp9/encoder/vp9_onyx_if.c
	vp9/vp9_dx_iface.c
	vpx/vpx_decoder.h
	vpx/vpx_external_frame_buffer.h
	vpx_scale/generic/yv12config.c
	vpxdec.c

Change-Id: I7434cf590f1c852b38569980e4247fad0d939c2e