Minor, delete useless utilities
Don't pass useless closure parameter to JetTypeMapper

It should always be recorded in BindingContext
Extract and use name-mapping method in JetTypeMapper

It doesn't ever make sense to create JVM method signatures with names that come
directly from descriptors; we need to map some of them (<get-?> for property
accessors, <anonymous> for local functions/lambdas)
Drop BothSignatureWriter.needGenerics

It's OK to always make JVM generic signature since it's already constructed at
the end anyway
Delete different mapSignature() overloads

JetTypeMapper now is fully aware of the name it should choose for the mapped
method. The only exception is SAM conversion in ClosureCodegen, where the name
must be replaced
Remove JetTypeMapper.mapConstructorSignature()

Move its code to mapSignature with the idea of a future unification of all
signature mapping