Stop using the value of PL_expect

Stop using the value of PL_expect

The changes in commits leading up to this one avoided unnecessary
PL_expect assignments that would soon be clobbered by this
‘PL_expect = PL_lex_expect’ that restores the previous value.

Hence, we no longer even need to read the value of PL_lex_expect since
PL_expect hasn’t changed.

Just one piece of code (KEY_package) was setting PL_lex_expect
directly instead of having force_next copy it from PL_expect, so this
commit changes it to set PL_expect to the correct value.