Remove gcc_version from gyp and gn files.

We used this to check if gcc is newer than 4.8 which is now required.
Remove the plumbing for this until we need to check gcc compiler versions
again, if ever.

No behavior change.

BUG=573778

Review URL: https://codereview.chromium.org/1577093002

Cr-Commit-Position: refs/heads/master@{#368706}
7 files changed