drop gridmap-file support

[kofemann]

The multimap gPlazma covers the the functionality that is provided by gridmap-file. Thus, it makes no sense to keep two plugins with the same functionality. THe migration should be trivial:

gridmap-file

# gmplazma.conf
map     optional    gridmap

# gridmap-file
"/C=DE/ST=Hamburg/O=dCache.ORG/CN=Kermit the frog" kermit

multimap

# gmplazma.conf
map     optional    multimap

# multimap
"dn:/C=DE/ST=Hamburg/O=dCache.ORG/CN=Kermit the frog" username:kermit