Remove outdated Mercurial repos from README.
Remove outdated Mercurial repos from README.

The Google Code and Bitbucket repositories have not been recently
updated. People who attempt to checkout the application from them will
receive outdated versions.

nidhi-delhivery/django-axes,svenhertle/django-axes,SteveByerly/django-axes,grue/django-axes,SteveByerly/django-axes,zoten/django-axes,jazzband/django-axes,django-pci/django-axes