libgsmhr1/dec_func.c: rm unused static functions In the original code, sp_dec.c held two kinds of functions: those needed only as part of the decoder, and those used by both decoder and encoder engines. In this library, we have moved the latter class of functions to dec_func.c module. Almost all static functions from the original sp_dec.c, with the exception of aToRc(), are needed only on sp_dec.c side of the new divide - remove them from dec_func.c, where they became dead code.

All Themyscira GSM codec libraries (currently libgsmefr, libgsmfr2 and libtwamr)
use Semantic Versioning, as described at <https://semver.org/>.  In the present
source release package, the semantic versions of the included libraries are as
follows:

libgsmefr version 1.2.0
libgsmfr2 version 2.1.0
libtwamr  version 1.0.0