ART: Delete catch phis for undefined vregs.

SSA builder assumed that (eagerly created) catch phis for undefined
vregs must be dead and will be deleted by dead phi elimination. This,
however, does not hold for --debuggable because the catch phis might
be revived for their environment uses. This patch modifies the builder
to delete the phis itself.

Bug: 24054676
Change-Id: Iaa5f2487ff1c38353b44cb89c709bbff1ecd73cc