Remove obsolete scripts

They are of course still in the Git history, and thus still preserved
in case they are ever needed again.
get-duplicate-class-names.sh: migrate to scijava

This script is general and useful enough to live in
scijava-common rather than imagej:
https://github.com/scijava/scijava-common/blob/dce336758c1c8d9b3c475ab8b82789321ced6c4c/bin/duplicate-class-names.sh