PPC: Remove obsolete functionality from the MacroAssemblers.

PPC: Remove obsolete functionality from the MacroAssemblers.

Port 64e3bad3677d01d70ddcedd541619216b973e90d

Original commit message:
    This is uncontroversial the dead code removal part of
    https://codereview.chromium.org/1307943013, which was
    previously landed, but got reverted because of DOM
    breakage that requires more investigation.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Committed: https://crrev.com/af6736779875a88f305cb86843705a3b47eb1373
Cr-Commit-Position: refs/heads/master@{#30590}

[JoranSiu, 2015-09-03 22:36:58]

lgtm

[MTBrandyberry, 2015-09-04 13:37:48]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-09-04 13:37:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1311123004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1311123004/1

[commit-bot: I haz the power, 2015-09-04 14:03:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-04 14:03:38]

Patchset 1 (id:??) landed as
https://crrev.com/af6736779875a88f305cb86843705a3b47eb1373
Cr-Commit-Position: refs/heads/master@{#30590}