Stop emitting the instructions INST_*_SCALAR_STK*.  They are identical to
their INST_*_STK* counterparts.
Having done that, it is clear the "simpleVarName" return from TclPushVarName
provides nothing of use to any of its callers.  Eliminate that.  Also make
TPVN return void, instead of int.
Bring the TPVN header comments up to date; they were quite rotten.