Directional predictors for 45, 63 and 207 angle had 2 or 3 variants
each, and only one of them was actually being used. So, removed the
C, sse2, ssse3 and neon versions of the unused ones.

Updates to the test:
- test_intra_pred_speed was testing the unused versions, so changed
  it to use the version actually used by code. This meant updating
  some golden MD5 values.
- test_intra_pred_speed was NOT filling up bottom-left and top-right
  pixels randomly, so the predictors using these pixels weren't tested
  properly. This was fixed.

BUG=aomedia:442

Change-Id: I09725d593408b81e0cd636e70a88c28eea5f2222