BugPoint: Fix some memory leaks.

Patch by Kostya Serebryany.

unique_ptr would be nice, but it's a bit too much work for an area I'm
not familiar with, nor invested in, unfortunately.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207265 91177308-0d34-0410-b5e6-96231b3b80d8