Drop rb5-userdebug build target and use db845c-userdebug for RB5

We have been using db845c-userdebug target builds to support
DB845c (RB3) and RB5 devboards for a long time now. So it is
time to formally drop rb5-userdebug build target from AOSP.

The RB5 flashing instructions in installer/rb5/ remain the same.
The device documentation as available from "Android Reference
Boards" page https://source.android.com/docs/setup/create/devices
is already updated.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: I2af594bfd23f7b963d65e9b50a38389b292f56cf
diff --git a/installer/rb5/README b/installer/rb5/README
index ee59bdb..fc9ae1d 100644
--- a/installer/rb5/README
+++ b/installer/rb5/README
@@ -2,7 +2,7 @@
 and AOSP images(built from sources) on rb5.
 
 First, make sure you have built the AOSP images for RB5 by
-running the rb5-userdebug lunch target.
+running the db845c-trunk_staging-userdebug lunch target.
 
 
 Boot the board into fastboot mode: