Various memory leak fixes in Vulkan

BUG=skia:6101

Change-Id: Iee798dd2d9dcc4521f643b814e65029b9383cc6f
Reviewed-on: https://skia-review.googlesource.com/6696
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
3 files changed