[SM17] Remove ratType field in MobileBytesTransfer(ByFgBg)

Currently, ratType field has been added into
MobileBytesTransfer(ByFgBg) atoms. However, add such dimension
is not backward compatible since callers might expect a complete
NetworkStats for specific uid in the metrics, but actually
the NetworkStats were distributed into metrics with
different ratType.

This change provide minimum modification that reverts the
behavior of MobileBytesTransfer, but related APIs will be needed
in subsequent changes.

Test: adb shell cmd stats pull-source 10000~10003
Test: atest android.cts.statsd.atom.UidAtomTests#testMobileBytesTransfer
Test: atest android.cts.statsd.atom.UidAtomTests#testMobileBytesTransferByFgBg
Bug: 129082217
Change-Id: I591f9fff2322c343479eb8587f14e48f878080b4