cmd/gomobile: remove binary XML

It is a full of unused code. Remove it.

Change-Id: I086f244adde57c8c9f1fc73b46e25550f15562f7
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/369197
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: changkun