Revert "vp9-svc: Fix speed issue with source downscaling for spatial layers."

This reverts commit f51f0998e1ca99cd7497ded3642bb27445b1b215.

This causes datarate tests to fail. Some are due to the new default
keyframe distance, another causes an assert even forcing 9999:

[ RUN      ] VP9/DatarateOnePassCbrSvc.OnePassCbrSvc3SpatialLayers/0
test_libvpx:
vpx_dsp/x86/vpx_subpixel_8t_intrin_ssse3.c:853: scaledconvolve2d:
Assertion `y_step_q4 <= 32' failed.

Change-Id: I4ee4fea97f47e4f1a23b82a62e6afc6280961e38
4 files changed