Remove dynamic allocation/indirection from GCOVBlocks owned by GCOVFunction

Since these are all created in the DenseMap before they are referenced,
there's no problem with pointer validity by the time it's required. This
removes another use of DeleteContainerSeconds/manual memory management
which I'm cleaning up from time to time.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224744 91177308-0d34-0410-b5e6-96231b3b80d8