Move <uses-sdk /> to a differnt XML

Basically Android Studio does want targetSdkVersion to be specified in
build.gradle rather than AndroidManifest.xml.  To make both make build
and Android Studio build happy, this CL splits <uses-sdk /> from the
main AndroidManifest.xml to a different file and let them merged in
make build.

There should be no behavior change.

Bug: 110741422
Test: Manually verified that there is no difference in
      AndroidManifest.xml in the APK.
Change-Id: Ib673bca5a31b2f95329c9310a127ec0701bd8fdc