Revert addition of a few fixed_dsp functions to APIChanges

The header is not installed currently so the changes should not be in APIChanges

Found-by: Ronald S. Bultje and others
This reverts part of commit 19ed3e35a5.

doc/APIchanges

@@ -15,13 +15,6 @@ libavutil:     2014-08-09
 
 API changes, most recent first:
 
-2015-06-05 - xxxxxxx - lavu  54.27.100 - fixed_dsp.h
-  Add vector_fmul()
-  Add vector_fmul_reverse()
-  Add vector_fmul_add()
-  Add scalarproduct_fixed()
-  Add butterflies_fixed()
-
 2015-06-04 - xxxxxxx - lswr  1.2.100
   Add swr_get_out_samples()