symb: Don't bother updating attribs/stats in symbDelVar()

The FBSYMBOL will be free'ed, so the fields can't be read later anyways.
symb: Ensure wstring literals are free'ed properly even with CONST bits
symb: Remove symbGetArrayOffset(), is just an alias for symbGetArrayDiff()
symb: Ensure symbAddVar() and symbAddField() initialize all VAR fields
symb: Solve out unnecessary parameter of symbAddArrayDesc()
symb: Re-use symbVarInitFields() in symbAddArrayDesc()
symb: Re-use symbSetArrayDimTb() in symbAddField()
symb: Make symbAddArrayDim() private
symb: Remove unused overload of symbCalcArrayElements()