Revert "Update fontconfig to 6cc99d6a"

This reverts commit e6db40d91d0bd2afeb39f78f6d22404c3525b63c.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 567445 as the
culprit for failures in the build cycles as shown on:
https://findit-for-me.appspot.com/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtL2U2ZGI0MGQ5MWQwYmQyYWZlYjM5Zjc4ZjZkMjI0MDRjMzUyNWI2M2MM

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.linux/Linux%20Builder%20%28dbg%29%2832%29/83483

Sample Failed Step: compile

Original change's description:
> Update fontconfig to 6cc99d6a
> 
> Changelog [1].  This is necessary to pick up [2] for fixing undefined-shift
> UBSAN errors detected by clusterfuzz, [3] to allow removing a build workaround,
> [4] to fix a bug and clean up some log spam, [5] to fix CFI builds, and [6] to
> fix a use-after-free.
> 
> Fontconfig also now requires libuuid as a dependency, so whitelist it as a
> dependency since we statically link fontconfig.
> 
> [1] https://chromium.googlesource.com/external/fontconfig/+log/b546940435ebfb0df575bc7a2350d1e913919c34..6cc99d6a82ad67d2f5eac887b28bca13c0dfddde
> [2] https://chromium.googlesource.com/external/fontconfig/+/c60ed9ef66e59584f8b54323018e9e6c69925c7e
> [3] https://chromium.googlesource.com/external/fontconfig/+/b8a225b3c3495942480377b7b3404710c70be914
> [4] https://chromium.googlesource.com/external/fontconfig/+/7ad010e80bdf8e41303e322882ece908f5e04c74
> [5] https://chromium.googlesource.com/external/fontconfig/+/096e8019be595c2224aaabf98da630ee917ee51c
> [6] https://chromium.googlesource.com/external/fontconfig/+/6cc99d6a82ad67d2f5eac887b28bca13c0dfddde
> 
> BUG=831146,822737,787020,829890,847323
> TBR=thestig,dnicoara
> 
> Change-Id: Ic2d1bd19af8ca131c960a30d09246827c115ccec
> Reviewed-on: https://chromium-review.googlesource.com/1095538
> Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
> Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#567445}

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
BUG=831146,822737,787020,829890,847323

Change-Id: I47d475941350efc76370fa5eb5043c80c5063495
Reviewed-on: https://chromium-review.googlesource.com/1101759
Cr-Commit-Position: refs/heads/master@{#567472}