Add Test::ReportPrereqs in SEE ALSO (RT#83266)

Thanks David Golden.
avoid needless spam during development by making the test not run during AUTHOR_TESTING
remove unused dependency
s/Test::Differences/Test::Deep

Test::Deep is RJBS-ware, better maintained than Test::Differences, and is also
not broken on TB2/Test::Builder 1.005+.
Make the skip-when-author-testing feature configurable, defaulting to off.