Two useless/empty bison reductions removed.
The useless reductions corresponded to parameter declarator lists, and
were detected due to uselessness detection (by linters) from previous
commit, yet couldn't be removed then because removing them triggerred a
hidden bug (which I didn't want to fix in that commit). This fix
propperly handles the fuzzy logic of the parameter declaration style
(unknown, new or old).
This change decreaseases the number of reduce/reduce conflicts but
increases the number of shift/reduce ones (which is in line with bison's
manual urging for removal/minimization of reduce/reduce conflicts).