[AsmPrinter] .addrsig_sym: remove isTransitiveUsedByMetadataOnly

With D135642 ignoring unregistered symbols, isTransitiveUsedByMetadataOnly added
by D101512 is no longer needed (the operation is potentially slow). There is a
`.addrsig_sym` directive for an only-used-by-metadata symbol but it does not
emit an entry.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D138362