We can't do direct calls via the .long sym hack, since that is
normally for an absolute relocation, but calls are expecting
relative relocations (except for reg/mem forms).

Nop-out the InstFake emitIAS methods. Remove the generic dispatcher
that redirects emitIAS() to emit(), since only branches and labels
are left.

BUG=none
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/647193003