liblp: Force 10.0 metadata on downgrade to Q.

Q liblp only supports 10.0 super partition metadata, so
forcefully downgrade the current metadata version too.

On retrofit Virtual A/B devices, the metadata version is
at most 10.1, because the new VIRTUAL_AB flag is not set
on retrofit devices.

In version 10.1, two per-partition flags: UPDATED and DISABLED
are introduced.
- The updated flag is set when the device undergoes a Virtual A/B
update before. Clear it.
- The disabled flag should only be set on metadata files used by
libfiemap ImageManager. It shouldn't be used on super partition metadata.

Hence, this CL should only clear UPDATED flag.

Test: R->R->Q OTA
Bug: 159590481
Change-Id: I8b548c8ce36a75197e7172a77f9207fd44fe4670