Update release instructions for new Github branch protection rules. (#1430)

Now protected branches can be specified with a pattern, so we can protect all
release branches with one rule. See
https://help.github.com/articles/about-protected-branches/.  There is no need to
enable branch protection when making a release.
diff --git a/RELEASING.md b/RELEASING.md
index 393bb3a..4598f7d 100644
--- a/RELEASING.md
+++ b/RELEASING.md
@@ -71,27 +71,10 @@
     $ git checkout -b v$MAJOR.$MINOR.x master
     $ git push upstream v$MAJOR.$MINOR.x
     ```
+    The branch will be automatically protected by the GitHub branch protection rule for release
+    branches.
 
-2. Enable branch protection for the new branch, if you have admin access.
-   Otherwise, let someone with admin access know that there is a new release
-   branch.
-
-    - Open the branch protection settings for the new branch, by following
-      [Github's instructions](https://help.github.com/articles/configuring-protected-branches/).
-    - Copy the settings from a previous branch, i.e., check
-      - `Protect this branch`
-      - `Require pull request reviews before merging`
-      - `Require status checks to pass before merging`
-      - `Include administrators`
-
-      Enable the following required status checks:
-      - `cla/google`
-      - `continuous-integration/appveyor/pr`
-      - `continuous-integration/travis-ci`
-    - Uncheck everything else.
-    - Click "Save changes".
-
-3.  For `master` branch:
+2.  For `master` branch:
 
     -   Change root build files to the next minor snapshot (e.g.
         `0.5.0-SNAPSHOT`).
@@ -113,7 +96,7 @@
     $ git push upstream master
     ```
 
-4.  For `vMajor.Minor.x` branch:
+3.  For `vMajor.Minor.x` branch:
 
     -   Change root build files to remove "-SNAPSHOT" for the next release
         version (e.g. `0.4.0`). Commit the result and make a tag: