android: configs: Remove CONFIG_USB_G_ANDROID from base.

3.18 supports configfs so it doesn't make sense to require
G_ANDROID. Devices using configfs should be allowed to turn
this off.

This fixes 3.18 emulator build.

Bug: 63996569
Change-Id: Ic0573f9f8564e9026ddbc50d340a0716285ecb04
Signed-off-by: Jerry Zhang <zhangjerry@google.com>