Reword "corresponding function templates"

[tkoeppe]

    1. It should presumably be "two _declarations of_ function templates", since it is declarations that correspond (and the bullet immediately above says that they declare something).

1. Is the idea that we should explicitly refer to satisfaction of the constraints? We already have in [temp.over.link]/6.4 that a template-head can be "satisfied".

Originally posted by @opensdh in #5984 (comment)