Delete loopfilter_avx2.c
Delete loopfilter_avx2.c

Not used.

Change-Id: I9f87a0ba54c603e622aad3f5c88bc1e7bfa76190

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