Up until now, there were four copies of
quantize_and_encode_band_cost_(ZERO|[SU]QUAD|[SU]PAIR|ESC|NONE|NOISE|STEREO)
(namely in aaccoder.o, aacenc_is.o, aacenc_ltp.o, aacenc_pred.o).
As 43b378a0 says, this is meant to
enable more optimizations.

Yet neither GCC nor Clang performed such optimizations: The functions
in the aforementioned files are not optimized according to
the specifics of the calls in the respective file. Therefore
duplicating them is a waste of space; this commit therefore stops doing
so. The remaining copy is placed into aaccoder.c (which is the only
place where the "round to zero" variant of quantize_and_encode_band()
is used, so that this can be completely internal to aaccoder.c).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>