remove file size limit on GVC config

remove file size limit on GVC config

While it is probably not a good idea to have a GVC config that is 100000 bytes,
I see no reason it should be arbitrarily rejected. In future, it might be a good
idea to make `gvconfig_plugin_install_from_config` accept a file pointer instead
of a string and read/parse the config file incrementally. If this were done,
then there would probably be no issue at all with large configs.