Remove GTK2 code

GTK2 code was historically kept around to keep the electron build working.  But
as of Nov 26, 2017, electron now uses GTK3 [1], so it should now be safe to
remove all of the old GTK2-only code.

[1] https://github.com/electron/electron/issues/2927#issuecomment-347092515

BUG=876558
R=sky

Change-Id: I78402053ae508ccd8fc7ac73697a861bb1ebacf6
Reviewed-on: https://chromium-review.googlesource.com/1183858
Commit-Queue: Thomas Anderson <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Cr-Commit-Position: refs/heads/master@{#585265}
diff --git a/docs/linux_debugging.md b/docs/linux_debugging.md
index aff0dd77..c69b0fa 100644
--- a/docs/linux_debugging.md
+++ b/docs/linux_debugging.md
@@ -453,7 +453,7 @@
 
 Note that the `--lang` flag does **not** work properly for this.
 
-On non-Debian systems, you need the `gtk20.mo` files. (Please update these docs
+On non-Debian systems, you need the `gtk30.mo` files. (Please update these docs
 with the appropriate instructions if you know what they are.)
 
 ## Breakpad