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_build_instructions.md b/docs/linux_build_instructions.md
index 4803829..36dcbd72c 100644
--- a/docs/linux_build_instructions.md
+++ b/docs/linux_build_instructions.md
@@ -340,7 +340,7 @@
 
 ```shell
 $ sudo pacman -S --needed python perl gcc gcc-libs bison flex gperf pkgconfig \
-nss alsa-lib glib2 gtk2 nspr ttf-ms-fonts freetype2 cairo dbus libgnome-keyring
+nss alsa-lib glib2 gtk3 nspr ttf-ms-fonts freetype2 cairo dbus libgnome-keyring
 ```
 
 For the optional packages on Arch Linux:
@@ -389,7 +389,7 @@
 su -c 'yum install git python bzip2 tar pkgconfig atk-devel alsa-lib-devel \
 bison binutils brlapi-devel bluez-libs-devel bzip2-devel cairo-devel \
 cups-devel dbus-devel dbus-glib-devel expat-devel fontconfig-devel \
-freetype-devel gcc-c++ glib2-devel glibc.i686 gperf glib2-devel gtk2-devel \
+freetype-devel gcc-c++ glib2-devel glibc.i686 gperf glib2-devel \
 gtk3-devel java-1.*.0-openjdk-devel libatomic libcap-devel libffi-devel \
 libgcc.i686 libgnome-keyring-devel libjpeg-devel libstdc++.i686 libX11-devel \
 libXScrnSaver-devel libXtst-devel libxkbcommon-x11-devel ncurses-compat-libs \
@@ -423,8 +423,7 @@
 ```
 
 For 11.0, use `libnspr4-0d` and `libnspr4-dev` instead of `mozilla-nspr` and
-`mozilla-nspr-devel`, and use `php5-cgi` instead of `php5-fastcgi`. And need
-`gtk2-devel`.
+`mozilla-nspr-devel`, and use `php5-cgi` instead of `php5-fastcgi`.
 
 (openSUSE 11.0)
 
@@ -432,7 +431,7 @@
 sudo zypper in subversion pkg-config python perl \
      bison flex gperf mozilla-nss-devel glib2-devel gtk-devel \
      libnspr4-0d libnspr4-dev wdiff lighttpd gcc gcc-c++ libexpat-devel \
-     php5-cgi alsa-devel gtk2-devel jpeg-devel
+     php5-cgi alsa-devel gtk3-devel jpeg-devel
 ```
 
 The Ubuntu package `sun-java6-fonts` contains a subset of Java of the fonts used.