Better overload-removal API in Parse

Previously, one could only remove mappings from strings to bare terms,
making it hard to remove overloadings to patterns. Now it is possible
to remove pattern overloadings too.

Illustrate new facility with example of fixing record field updates to
be less polymorphic.

Better overload-removal API in Parse

Previously, one could only remove mappings from strings to bare terms,
making it hard to remove overloadings to patterns. Now it is possible
to remove pattern overloadings too.

Illustrate new facility with example of fixing record field updates to
be less polymorphic.