Move/deduplicate util functions to libff

[alexander-zw]

Some functions in libiop are duplicated in libff. They should be removed from libiop and all usages should refer to the corresponding functions in libff. This includes the functions in profiling.hpp and the UNUSED macro.

Some other functions are present only in libiop and not libff, but make more sense in libff. This includes the functions in field_utils.cpp as well as power and enable_if. These should be moved accordingly.

Note: Some of this duplication may also be present in libfqfft but that is outside of the scope of this issue.