[flang] Remove materialization workaround in type converter (#98743)

This change is in preparation of #97903, which adds extra checks for
materializations: it is now enforced that they produce an SSA value of
the correct type, so the current workaround no longer works.

The original workaround avoided target materializations by directly
returning the to-be-converted SSA value from the materialization
callback. This can be avoided by initializing the lowering patterns that
insert the materializations without a type converter. For
`cg::XEmboxOp`, the existing workaround that skips
`unrealized_conversion_cast` ops is still in place.

Also remove the lowering pattern for `unrealized_conversion_cast`. This
pattern has no effect because `unrealized_conversion_cast` ops that are
inserted by the dialect conversion framework are never matched by the
pattern driver.

0 files changed, 0 insertions, 0 deletions