[MCJIT] Delete the JTIMemoryManager and associated APIs.

[MCJIT] Delete the JTIMemoryManager and associated APIs.

This patch removes the old JIT memory manager (which does not provide any
useful functionality now that the old JIT is gone), and migrates the few
remaining clients over to SectionMemoryManager.

http://llvm.org/PR20848

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218316 91177308-0d34-0410-b5e6-96231b3b80d8