[Support] Remove MemoryBuffer::getNewMemBuffer

all callers have been switched the the Writable version (which does not
require const_casting to be useful).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322475 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed