Android: Update docs to say Java 8 is required

docs/android_build_instructions.md

 # Checking out and building Chromium for Android
 
 There are instructions for other platforms linked from the
 [get the code](get_the_code.md) page.
 
 ## Instructions for Google Employees
 
 Are you a Google employee? See
 [go/building-chrome](https://goto.google.com/building-chrome) instead.
 
@@ skipping 94 matching lines @@
 
 ```shell
 $ gclient runhooks
 ```
 
 *Optional*: You can also [install API
 keys](https://www.chromium.org/developers/how-tos/api-keys) if you want your
 build to talk to some Google services, but this is not necessary for most
 development and testing purposes.
 
-### Configure the JDK
-
-Make also sure that OpenJDK 1.7 is selected as default:
-
-```shell
-$ sudo update-alternatives --config javac
-$ sudo update-alternatives --config java
-$ sudo update-alternatives --config javaws
-$ sudo update-alternatives --config javap
-$ sudo update-alternatives --config jar
-$ sudo update-alternatives --config jarsigner
-```
-
 ## Setting up the build
 
 Chromium uses [Ninja](https://ninja-build.org) as its main build tool along
 with a tool called [GN](../tools/gn/docs/quick_start.md) to generate `.ninja`
 files. You can create any number of *build directories* with different
 configurations. To create a build directory which builds Chrome for Android,
 run:
 
 ```shell
 $ gn gen --args='target_os="android"' out/Default
@@ skipping 238 matching lines @@
 release of Chrome for Android (v25+) you can do the following steps.
 Note that in order to get your changes into the official release, you'll
 need to send your change for a codereview using the regular process for
 committing code to chromium.
 
 1.  Open Chrome on your Android device and visit chrome://version
 2.  Copy down the id listed next to "Build ID:"
 3.  Go to
     [http://storage.googleapis.com/chrome-browser-components/BUILD\_ID\_FROM\_STEP\_2/index.html](http://storage.googleapis.com/chrome-browser-components/BUILD_ID_FROM_STEP_2/index.html)
 4.  Download the listed files and follow the steps in the README.