drm_hwcomposer: Remove hwc2 build targets
All devices in aosp have been migrated to hwc3. Remove the hwc2 build targets as a first step towards removing hwc2 from this project.
Change-Id: I116e4d13342368e9375b4d96d9598ba058f936a0 Signed-off-by: Drew Davenport ddavenport@google.com