Remove operator_area note from godoc overview

[freddygv]

Currently the following note about operator areas shows up as the godoc synopsys for Consul:

The /​v1/​operator/​area endpoints are available only in Consul Enterprise and interact with its network area subsystem.

This is because it is the only comment above the api package declaration.

This PR moves the comment below package api since the note applies to the whole file but should not be pulled into godoc.

[mkeeler]

Good catch