Remove fetching of pInterp. Currently, there's no actual effect other
than to store the location of a forth word that is subsequently never
used. It was last used before the 2.03 ficl upgrade in r51786. It was
only used from r43614 (so Feb-Sept 1999) on head and in the 3.x branch
(merged r43715 3.1 -> EOL). Remove it since nobody cared enough to
report the bug in the last 18 years rather than fix it. It's need
seems to have passed in the 2.03 ficl update.

Differential Revision: https://reviews.freebsd.org/D8150