Removed GroupM as alias of PubMatic (#3761)
Removed GroupM as alias of PubMatic (#3761)

* removed groupm docs

* Updated docs for groupm

* adding version note header

Co-authored-by: pm-azhar-mulla <e06d6e729196c564869a2c58b1ba7b1454a04b25@L1119.local>
Co-authored-by: bretg <9df09da23577b88db5b6b8911d0635d4f870e78e@gmail.com>
prebid/prebid.github.io,prebid/prebid.github.io,prebid/prebid.github.io