Correct docstring for salt.modules.dnsutil.hosts_remove

It looks like this function might have changed names at one point and
the docstring was never updated, or the docstring was just incorrect to
begin. This fixes CLI example to match the correct function name.

Resolves #7255.
Merge pull request #7262 from terminalmage/issue7255

Correct docstring for salt.modules.dnsutil.hosts_remove