These tests can't be fully enabled until this is fixed:
rdar://147194789 ([nonescapable] 'mutating get' causes a type checking error for
non-existent _read accessor)
Needed to diagnose MutableSpan and OutputSpan.
For now, simply remove the bailout and TODO. The next change will introduce more
logic to force a diagnostic error in rare cases that can't be handled completely.
Fixes rdar://143584461 (Extended exclusive borrow issues with
MutableSpan and OutputSpan)
