Revert "adb: support /oem partition"

This is broken on userdebug builds, and it isn't completely clear why. The declaration for make_block-device_writable in adb.h wasn't updated to match the definition (which uses a std::string instead of a char*). adb.h is currently extern "C", and it isn't clear why this is only broken for userdebug, so I'd like to revert while we investigate.

This reverts commit 81416fdb.

Change-Id: I47f321574f9f21052e2c7332e8b0f6ef9ab98277