docs: get rid of git-svn note

docs/mac_build_instructions.md

 # Mac Build Instructions
 
 [TOC]
 
 ## Prerequisites
 
 *   A Mac running 10.9+.
 *   https://developer.apple.com/xcode, 5+
 *   Install
     [gclient](http://dev.chromium.org/developers/how-tos/install-depot-tools),
     part of the
     [depot_tools](http://dev.chromium.org/developers/how-tos/depottools) package
     ([download](http://dev.chromium.org/developers/how-tos/install-depot-tools)).
     gclient is a wrapper around svn that we use to manage our working copies.
 *   Install Xcode's "Command Line Tools" via Xcode menu -> Preferences ->
     Downloads
 *   The OSX 10.10 SDK. Run
     ```sh
     ls `xcode-select -p`/Platforms/MacOSX.platform/Developer/SDKs
     ```
     to check whether you have it. If you don't have it, you need to get one from
     an install of Xcode 6, and place it in the above directory.
 
 ## Getting the code
 
 [Check out the source code](http://dev.chromium.org/developers/how-tos/get-the-code)
-using Git. If you're new to the project, you can skip all the information about
-git-svn, since you will not be committing directly to the repository.
+using Git.
 
 Before checking out, go to the
 [waterfall](http://build.chromium.org/buildbot/waterfall/) and check that the
 source tree is open (to avoid pulling a broken tree).
 
 The path to the build directory should not contain spaces (e.g. not
 `~/Mac OS X/chromium`), as this will cause the build to fail. This includes your
 drive name, the default "Macintosh HD2" for a second drive has a space.
 
 ## Building
@@ skipping 188 matching lines @@
 be set in `/etc/sysctl.conf`:
 
     echo kern.maxvnodes=$((512*1024)) | sudo tee -a /etc/sysctl.conf
 
 Or edit the file directly.
 
 If your `git --version` reports 2.6 or higher, the following may also improve
 performance of `git status`:
 
     git update-index --untracked-cache