This reverts commit 2bf23ea8.

Reason for revert: Probably not the right fix. Will export
all angle_utils symbols in places where they shouldn't be.

Original change's description:
> util: Always specify default visibility on exports.
> 
> This fixes undefined behaviour with CFI.
> 
> Bug: chromium:1015810
> Bug: angleproject:3162
> Change-Id: I58cfb78adabbff05e5b4560dfd70b190411fa26d
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1869303
> Reviewed-by: Jamie Madill <jmadill@chromium.org>
> Commit-Queue: Jamie Madill <jmadill@chromium.org>

TBR=ynovikov@chromium.org,jmadill@chromium.org

Change-Id: Ie847a9e6506178eb2b14e63a1ee5e9a1775b4548
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1015810, angleproject:3162
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1869546Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>