Deprecate Always_use_prebuilt_sdks.Enabled

This property is not evaluated in Soong's prebuilt mutators, which can
cause duplicate installation errors.

Please use `build/soong/docs/selects.md` for `Enabled` property.

Test: m nothing --no-skip-soong-tests
Bug: 403514488
Change-Id: I7fbdc8db8d72543a3e31169bb9fb4b77c3d5c108