Re-enable test_convenience_registers_16bit_with_process_attach test for Linux.
Remove 32-bit POSIX register hack in ConvertBetweenRegisterKinds.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@192306 91177308-0d34-0410-b5e6-96231b3b80d8