[opt] Remove the ExternalFunctionsPassedConstants pass

This commit is removing the last pieces of AnalysisWrapper.cpp
(including the ExternalFunctionsPassedConstants pass, aka
print-externalfnconstants).

The pass only existed for the legacy PM, and it was not regression
tested. And since the pass did not force the use of the legacy pass
manager there was no simply way to run the pass nowadays, at least
not by using opt.

Differential Revision: https://reviews.llvm.org/D148081