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

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

This reverts commit 66ba71d9.

Addressing issues found by:
https://lab.llvm.org/buildbot/#/builders/245/builds/11732
https://lab.llvm.org/buildbot/#/builders/187/builds/12251
https://lab.llvm.org/buildbot/#/builders/186/builds/11099
https://lab.llvm.org/buildbot/#/builders/182/builds/6976