Adapters Should not Require Hostname Parameter

[ChrisHuie]

Currently it looks like Adkernel is requiring hostname as a parameter in their bid adapter. It is felt this is unreasonable because it pushes too much complexity onto publishers. Instead, host should be an optional parameter that has a default in the adapter code.

Statement on requiring hostname in recent alias addition to docs -> prebid/prebid.github.io#5790.

[patmmccann]

see also #12483 (comment)