[CSSPGO] Do not use getCanonicalFnName in pseudo probe descriptor decoding

Pseudo probe descriptors are created very early in the pipeline where function names just come from the front end and are not yet decorated. So calling getCanonicalFnName on the function names in probe desc is basically a no-op, which also addes a depenency from MC to ProfileData unnessesarily.

Reviewed By: wenlei, wlei

Differential Revision: https://reviews.llvm.org/D107838