Remove ApexBundleDepsInfo.MinSdkVersion()

For java.AndroidApp app, app.MinSdkVersion() was selected from
ApexBundleDepsInfo, not from java.Module.
This caused app.MinSdkVersion() to return "" always.

Besides, having two embeded fields and relying on depth to choose one of
them makes it hard to read.

Bug: 156537348
Test: m
Change-Id: Ib525b2f5132c596db8e33492d0a565ea23e91d1c