[es6] Fix and clean up recognition of simple parameter lists

[es6] Fix and clean up recognition of simple parameter lists

Gets rid of IsSimpleParameterList predicate.

R=mstarzinger@chromium.org, caitpotter88@gmail.com
BUG=

Committed: https://crrev.com/a10e877c3e6ffef3b15e433d888a719619116a42
Cr-Commit-Position: refs/heads/master@{#29815}

[Michael Starzinger, 2015-07-23 11:15:27]

LGTM.

[rossberg, 2015-07-23 11:58:23]

The CQ bit was checked by rossberg@chromium.org

[rossberg, 2015-07-23 11:58:23]

The patchset sent to the CQ was uploaded after l-g-t-m from
mstarzinger@chromium.org
Link to the patchset: https://codereview.chromium.org/1251603004/#ps20001
(title: "Rebase")

[commit-bot: I haz the power, 2015-07-23 11:58:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1251603004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1251603004/20001

[commit-bot: I haz the power, 2015-07-23 12:10:30]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-07-23 12:10:30]

Try jobs failed on following builders:
  v8_linux64_rel on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux64_rel/builds/7991)

[rossberg, 2015-07-23 14:03:39]

The CQ bit was checked by rossberg@chromium.org

[commit-bot: I haz the power, 2015-07-23 14:03:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1251603004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1251603004/20001

[commit-bot: I haz the power, 2015-07-23 14:29:04]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-07-23 14:29:17]

Patchset 2 (id:??) landed as
https://crrev.com/a10e877c3e6ffef3b15e433d888a719619116a42
Cr-Commit-Position: refs/heads/master@{#29815}