docs: simplify the gclient wording in mac_build_instructions.md

gclient is just part of a bigger package called 'depot_tools',
and a bunch of other tools from depot_tools are necessary to get
the job done, not just gclient. So like the iOS build instructions,
just point to depot_tools page.

BUG=None
R=sdefresne@chromium.org

Review URL: https://codereview.chromium.org/1760833002

Cr-Commit-Position: refs/heads/master@{#379002}

docs/mac_build_instructions.md

@@ -5,13 +5,8 @@
 ## Prerequisites
 
 *   A Mac running 10.9+.
-*   [Xcode](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.
+*   [Xcode](https://developer.apple.com/xcode) 5+.
+*   [depot\_tools](http://dev.chromium.org/developers/how-tos/depottools).
 *   Install Xcode's "Command Line Tools" via Xcode menu -> Preferences ->
     Downloads
 *   The OSX 10.10 SDK. Run