Set UNBUNDLED_BUILD_SDKS_FROM_SOURCE to true by default in

module_common.mk if the branch is not using slim manifests.
This makes sure that mainline modules build locally are
using the build from source sdk.

Bug: 262783668
Test: time m atest && time atest-dev CtsNetTestCasesLatestSdk[CaptivePortalLoginGoogle.apk+NetworkStackGoogle.apk+com.google.android.resolv.apex+com.google.android.tethering.apex] --verbose
Change-Id: I37b94448a45b0b811ae1815ad8c46589c62e8542
(cherry picked from commit 40e6f9bd)
Merged-In: I37b94448a45b0b811ae1815ad8c46589c62e8542