Revert "MIPS: add data tracing to the 32-bit MIPS simulator."

This pushed the simulator over 500 non-comment lines in
Simulator::DecodeTypeRegister(), which was rejected by presubmit.

In looking at the code, I realized I did not properly trace
newer r6 instructions, so I will have to refactor this and land
it as a separate CL.

This reverts commit c6c44f98ac4d6f1b014817b9bcf63823be818ec8.