Revert of Use sysroot by default for all linux builds

Revert of Use sysroot by default for all linux builds (patchset #7 id:120001 of https://codereview.chromium.org/1464983003/ )

Reason for revert:
Seems to have caused issues with goma: https://code.google.com/p/chromium/issues/detail?id=560973

Original issue's description:
> Use sysroot by default for all linux builds
>
> Using a sysroot was already the default for official
> build and when cross compiling (e.g. arm, mips, x86-32).
> This change makes it the default in all cases.
>
> The old behavior of building against local
> system libraries can still be achieved by
> setting use_sysroot=0
>
> BUG=504446
>
> Committed: https://crrev.com/a931efd5dc8d8783ce73a64fc641627866b6869d
> Cr-Commit-Position: refs/heads/master@{#361197}

TBR=dpranke@chromium.org,thestig@chromium.org,thakis@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=504446
Committed: https://crrev.com/05373dc078f0d5d3f2fb1398db9a4008a55d9016
Cr-Commit-Position: refs/heads/master@{#361405}

[Sam Clegg, 2015-11-24 18:50:45]

Created Revert of Use sysroot by default for all linux builds

[commit-bot: I haz the power, 2015-11-24 18:52:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1473363002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1473363002/1

[commit-bot: I haz the power, 2015-11-24 18:56:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-24 18:57:32]

Patchset 1 (id:??) landed as
https://crrev.com/05373dc078f0d5d3f2fb1398db9a4008a55d9016
Cr-Commit-Position: refs/heads/master@{#361405}

[Sam Clegg, 2015-11-24 19:24:41]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1472873004/ by sbc@chromium.org.

The reason for reverting is: Relanding sysroot change.