[BOLT] Get rid of Names in BinaryData

Summary:
For BinaryData, we used to maintain a vector of StringRef names and also
a vector of pointers to MCSymbol's associated with the data. There was
an unnecessary duplication of information and an associated overhead of
keeping it in sync. Fix it by removing Names and using Symbols wherever
Names were used.

Also merge two variants of registerNameAtAddress() and remove
unreachable/dead code in the process.

(cherry picked from FBD19359123)