This reverts commit 535b7b91.

This is actually used in CBR to reset the rate control if high source sad is detected.

Original change's description:
> Remove the speed condition on scene detection in 1 pass code.
> 
> Scene detection is used for VBR mode and for screen_content mode.
> 
> It was also enabled for CBR mode via the speed condition,
> but currently the analysis in the scene detection is not used
> in CRB mode (similar computations are done locally at superblock level
> when the source_sad feature is enabled).
> 
> For 1 pass code.
> No change in behavior. Small speed gain, ~0.5%.
> 
> Change-Id: I59991d7ef2af320bea7af4b907596e057affa42f

TBR=marpan@google.com,builds@webmproject.org,jianj@google.com

Change-Id: Ib4e6b02047f75632503e7b0fc870af97fa9291c3
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