Revert "[llvm-profdata] Refactoring Sample Profile Reader to increase FDO build speed...

Revert "[llvm-profdata] Refactoring Sample Profile Reader to increase FDO build speed using MD5 as key to Sample Profile map"

This reverts commit 31af18bccea95fe1ae8aa2c51cf7c8e92a1c208e.

This change is causing build failures on many Windows build bots:

https://lab.llvm.org/buildbot/#/builders/216/builds/22833
https://lab.llvm.org/buildbot/#/builders/123/builds/19602
https://lab.llvm.org/buildbot/#/builders/172/builds/28315
https://lab.llvm.org/buildbot/#/builders/119/builds/13870
https://lab.llvm.org/buildbot/#/builders/233/builds/794
https://lab.llvm.org/buildbot/#/builders/235/builds/387
https://lab.llvm.org/buildbot/#/builders/13/builds/36921
https://lab.llvm.org/buildbot/#/builders/127/builds/50510