Localize the use of CONFIG_EXT_DELTA_Q
Localize the use of CONFIG_EXT_DELTA_Q

The commit localizes the use of a experimental flag to reduce code
duplication.

BUG=aomedia:442

Change-Id: Ia9d5b28c5b1d8148e6ed5496b9cd135242e5c8d4

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom