ANDROID: db845c_gki.fragment: Remove modules built into GKI

The CONFIG_USB_EHCI_HCD and CONFIG_USB_EHCI_HCD_PLATFORM
values were moved into the gki_defconfig, so continuing to
build them as modules causes the resulting kernel to not boot.

This patch simply removes them.

Also drop the "CONFIG_USB_DUMMY_HCD is not set" override, as
its not doing anything other then causing warning on build.

Fixes: 953a6e32 ("ANDROID: GKI: support CONFIG_USB_EHCI_HCD_PLATFORM")
Fixes: bdb20ce7 ("ANDROID: GKI: support CONFIG_USB_EHCI_HCD")
Signed-off-by: John Stultz <john.stultz@linaro.org>
Change-Id: Ie53f6a1fb0c1a3c4ff6eef76c6b648600cdc7b2c