Remove all references to Mandel

[arhag]

Remove all references to Mandel or mandel from within the antelope-3.1 branch of leap.

Also, update the URLs referencing eosnetworkfoundation org repos to use the corresponding ones in the AntelopeIO organization. This applies also to the LICENSE files of the submodule repos referenced from the antelope-3.1 branch of leap. Note changes to the LICENSE files in the submodules should not be done directly on the main branch. It should be done on either the antelope-main or antelope-3.1 branch (whichever one exists). If neither exists, then create an antelope-main branch off of main and make those changes in the antelope-main branch.