[packages] python: Force usage of internal modules for hashlib instead of openssl

[packages] python: Force usage of internal modules for hashlib instead of openssl

Python can either use it's own implementation for the hashlib functions or it
can use openssl. If openssl is installed it will choose the openssl based
variant. But since openssl is not a dependency, but could have been build before
python we'll have to force the python build to choose the internal variant.

Fixes #6883

git-svn-id: svn://svn.openwrt.org/openwrt/packages@20372 3c298f89-4303-0410-b956-a3cf2f4a3e73