[imcc] fix more -O2 errors, found but empty => delete ins

On some constant propagation on (mostly arithmetic or param) ops,
the ins can be safely deleted. GH #1039

This fixed:
t/compilers/imcc/syn/macro.t 10-11
t/pmc/io.t 13-14
t/op/lexicals.t 42

but broke: t/pmc/exception-old.t 19