[NFC][SampleFDO] Clean the unneeded field and the related loop (#132376)
Clean the unneeded field 'TotalCollectedSamples' and the unnecessary
loop.
The field seems introduced in:https://reviews.llvm.org/D31952, and its
uses were removed in: https://reviews.llvm.org/D19287, but this field
and unnecessary calculation were not cleaned up.
This patch will remove these unneeded codes.