Revert "Mount generic ramdisk as readwrite."

This reverts commit 78b55b22.

Reason for revert: Replaced by Ib99aca13d4d:
ANDROID: GKI: build in a kernel command line of "rw"

Prebuilt is checked in at Ie34b5b017:
Update kernel to builds 6964541

Fixes: 171512004
Test: TH

Change-Id: I2aec88cc22483a6b3a671fc664d465624a14e5b0