Make android_build_instructions.md consistent about out/Default

There were a few places that used "out/Release", and one that used
"$gndir"

Change-Id: Ib2f75d0158335bcb9c0dda506c30657866b56336
Reviewed-on: https://chromium-review.googlesource.com/486251
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Yipeng Wang <yipengw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#467039}

docs/android_build_instructions.md

@@ -191,13 +191,13 @@ unplugging and reattaching your device.
 ### Build the full browser
 
 ```shell
-ninja -C out/Release chrome_public_apk
+ninja -C out/Default chrome_public_apk
 ```
 
 And deploy it to your Android device:
 
 ```shell
-CHROMIUM_OUTPUT_DIR=$gndir build/android/adb_install_apk.py $gndir/apks/ChromePublic.apk # for gn.
+build/android/adb_install_apk.py out/Default/apks/ChromePublic.apk
 ```
 
 The app will appear on the device as "Chromium".
@@ -209,12 +209,12 @@ Wraps the content module (but not the /chrome embedder). See
 for details on the content module and content shell.
 
 ```shell
-ninja -C out/Release content_shell_apk
-build/android/adb_install_apk.py out/Release/apks/ContentShell.apk
+ninja -C out/Default content_shell_apk
+build/android/adb_install_apk.py out/Default/apks/ContentShell.apk
 ```
 
 this will build and install an Android apk under
-`out/Release/apks/ContentShell.apk`. (Where `Release` is the name of your build
+`out/Default/apks/ContentShell.apk`. (Where `Release` is the name of your build
 directory.)
 
 If you use custom out dir instead of standard out/ dir, use