Update docs for the DFR similarity (#40579)
Update docs for the DFR similarity (#40579)

The basic models `b, de, p` and the after effect `no`
are not available anymore in Lucene 8 but they are still
listed in the >7x documentation. This change removes these
references that should also be listed in the breaking change
of es 7.0.

Closes #40264
coding0011/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,robin13/elasticsearch,HonzaKral/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch,coding0011/elasticsearch,HonzaKral/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch