Remove duplicate or unused code in encoder/encodemb.c.

Also make some minor stylistic changes to bring the code closer to
the style guide. Remove distinction between inter and intra transform
functions, since both do exactly the same thing except for the check
against SPLITMV for the second-order transform. Remove some commented
out debug code. Remove 8x8/16x16 transform code in encode_inter16x16y(),
since the first-pass only uses 4x4 anyway.

Change-Id: Ife54816ff759825b9141f95dc2ba43c253c14dba