Minor tweaks.

Minor tweaks.

Clean up replaceFailingInstruction() a little.  In particular, use
the appropriate method for extracting the opcode, and assert that
the instruction we're replacing was marked "can throw" (if it wasn't,
the list of predecessors in the catch handler will be wrong).  Also
remove a declaration that became redundant when we started replacing
instructions in place (as opposed to making a copy of the method body).

Strip out a bit of stale #if 0 code.

Change-Id: Iccf80647237672e2da4b1b46ca9627ae3344704d