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:
https://crbug.com/560603

Suspect this breaks webview_licenses

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,sbc@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=504446

[Steven Holte, 2015-11-24 01:45:39]

Created Revert of Use sysroot by default for all linux builds

[Lei Zhang, 2015-11-24 01:56:55]

https://codereview.chromium.org/1473533003 will fix the issue instead?