Remove unused glue layer code for postblit call

Now postblit call is properly done in front-end, so they are not needed anymore.
Reduce __inlineretval generation count

If nrvo_var != NULL, inlining can more directly replace it to the substituted variable.
Do inline for the variable initialization with NRVO function call

Pass `vret` as an additional inlining context, if it is found.