[CSSPGO] Skip dangling probe value when computing profile summary

Recently we switched to use InvalidProbeCount = UINT64_MAX (instead of 0) to represent dangling probe, but UINT64_MAX is not excluded when computing profile summary. This caused profile summary to produce incorrect hot/cold threshold. The change fixed it by excluding UINT64_MAX from summary builder.

Differential Revision: https://reviews.llvm.org/D99788