Remove WmShell's min_sdk and lint-baseline.xml

Removing min_sdk_version for WmShell since it's not meant to be backward
compatible.
Removing lint-baseline.xml which only contains "NewApi" errors, that
won't be generated now, since min_sdk_version has been removed.

Bug: 182759603
Test: make WmShell
Change-Id: I38e4814581d6c6a8aeb8d66b1b554a5bac331f68