[BOLT] Fix aggregator w.r.t. split functions

Summary:
We should not rely on split function detection while aggregating
data, but only look up the original function names in the symbol table.
Split function detection should be done by BOLT and not perf2bolt while
writing the profile. Then, BOLT, when reading it, will take care of
combining functions if necessary.

This caused a bug in bolted data collection where samples in cold parts
of a function were being falsely attributed to the hot part of a function
instead of being attributed to the cold part, causing incorrect translation of
addresses.

(cherry picked from FBD16993065)