Make Observer class as template Quant class for QuantConfig (#19418)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19418
This change makes Observer class template which always
takes an observer function as argument. Second test-case becomes redundant, hence removing
it.
Reviewed By: jerryzh168
Differential Revision: D15000594
fbshipit-source-id: 9555fe98a5f2054b8fd01e64e9ac2db72c043bfa
