ARM: dts: msm: Delete redundant USB nodes for SDX20

Currently both MDM9650 and SDX20 USB DT files are included
in SDX20 target DT files. This leads to warning of duplicate
sysfs directory creation because the address string for
USBBAM node is different. To get rid of this warning, delete
MDM9650 USB nodes and use SDX20 USB nodes only.

Change-Id: Iae39afa48594d1fa0ed76c33d03c89010f4b53b7
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>