Revert of Cherry pick disabled unicode compatibility decomposition into HarfBuzz

Revert of Cherry pick disabled unicode compatibility decomposition into HarfBuzz (patchset #1 id:1 of https://codereview.chromium.org/1416013004/ )

Reason for revert:
This change is causing bllink layout test failures on multiple platforms. Judging from the diffs, this looks like a regression, not just something that needs rebaselining.

fast/text/unicode-fallback-font.html (windows only)
fast/text/midword-break-before-surrogate-pair.html (windows only)
svg/text/non-bmp-positioning-lists.svg

Affected platforms:
Mac 10.6 only
Win XP, 7 and 10
Linux 64, 32 and Trusty

Original issue's description:
> Cherry pick disabled unicode compatibility decomposition into HarfBuzz
>
> HarfBuzz commit f6799700404c49ae0 disables unicode compatibility
> decomposition, avoiding undesirable substitutions and allowing Blink
> to fall back to system fonts for mathematical symbols and the
> like. Cherry-picking this into our HarfBuzz version in order to be able
> to land shaper driven segmentation.
>
> BUG=546454
> R=behdad,eae
>
> Committed: https://crrev.com/c6da2801d9e36a9f2bb5acf4e3c492c8f0680ad4
> Cr-Commit-Position: refs/heads/master@{#355551}

TBR=behdad@chromium.org,eae@chromium.org,drott@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=546454
Committed: https://crrev.com/4bd26388c7080027f1529dbee9730ed7f309cbbe
Cr-Commit-Position: refs/heads/master@{#355637}

[Justin Novosad, 2015-10-22 20:46:44]

Created Revert of Cherry pick disabled unicode compatibility decomposition into
HarfBuzz

[commit-bot: I haz the power, 2015-10-22 20:47:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1409993005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1409993005/1

[commit-bot: I haz the power, 2015-10-22 20:48:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-22 20:49:29]

Patchset 1 (id:??) landed as
https://crrev.com/4bd26388c7080027f1529dbee9730ed7f309cbbe
Cr-Commit-Position: refs/heads/master@{#355637}

[eae, 2015-10-22 21:54:55]

LGTM