ARM: dts: msm: remove redundant USB extcon on sm8150

The driver code now attempts to register both USB and USB_HOST
on each extcon phandle provided, so there is no need to specify
duplicate entries. Otherwise the same callbacks would end up
getting registered multiple times. Remove the duplicate
&pm855b_pdphy phandle from the USB node's extcon property.

Change-Id: I4039e4b3e4e50de18e28afb3230d5b9295aa58b0
Signed-off-by: Jack Pham <jackp@codeaurora.org>