[LLVM] remove extern template declarations of GenericCycleInfo

Having an extern template declaration prevents implicit instantiation of
templates, which causes linker errors when building with shared libraries. For
example, the sources in libAnalysis do not contain any explicit instantiation of
the CycleInfo, which is a specialization of GenericCycleInfo. Thus, any calls to
functions defined in the body of GenericCycleInfo produce undefined references.
The absence of any extern template declaration allows a local instance of these
functions to be created.