Flip Goma Linux x64 canary bots to GN.

We're long-past due for this ...

R=ukai@chromium.org
BUG=605732

Review URL: https://codereview.chromium.org/1915423002

Cr-Commit-Position: refs/heads/master@{#389825}

tools/mb/mb_config.pyl

@@ -113,9 +113,9 @@
       'CFI Linux CF': 'gn_cfi_diag_release_bot',
       'CFI Linux ToT': 'gn_cfi_release_bot',
       'CFI Linux': 'gn_cfi_release_bot',
-      'Chromium Linux Goma Canary': 'gyp_release_bot',
-      'Chromium Linux Goma Canary (clobber)': 'gyp_release_bot',
-      'Chromium Linux Precise Goma LinkTest': 'gyp_release_bot',
+      'Chromium Linux Goma Canary': 'gn_release_bot',
+      'Chromium Linux Goma Canary (clobber)': 'gn_release_bot',
+      'Chromium Linux Precise Goma LinkTest': 'gn_release_bot',
       'Chromium Linux32 Goma Canary (clobber)': 'gyp_release_bot_x86',
       'Chromium Mac 10.10 MacViews': 'mac_views_browser_gyp_release_bot',
       'Chromium Mac 10.11': 'gyp_release_bot',