Address warnings in EmulateInstructionARM64

- Remove default for switch which covers all enumeration values

- Remove unused functions
  LSL_C is left in the source under #if 0, as it may be needed in the
  future for emulating other instructions.

Differential Revision: http://reviews.llvm.org/D3528


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@207449 91177308-0d34-0410-b5e6-96231b3b80d8