Remove obsolete GN check.md documentation.

This information is covered in the built-in help under "gn help check" and "gn
help nogncheck".

R=estade@chromium.org
BUG=682331

Review-Url: https://codereview.chromium.org/2647443003
Cr-Original-Commit-Position: refs/heads/master@{#444492}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6c0a0762e46562f77c65b65a4dca2c6c296ba4d8
2 files changed
tree: a40152ec53a060b0ad8b064183c4707f74a51395
  1. tools/