Rename `org-format-agenda-item' to `org-agenda-format-item'.
* org.el (org-format-agenda-item, org-scan-tags): Rename
`org-format-agenda-item' to `org-agenda-format-item'.
* org-agenda.el (org-search-view)
(org-get-entries-from-diary, org-agenda-get-todos)
(org-agenda-get-timestamps, org-agenda-get-sexps)
(org-agenda-get-progress, org-agenda-get-deadlines)
(org-agenda-get-scheduled, org-agenda-get-blocks)
(org-agenda-format-item, org-agenda-add-time-grid-maybe)
(org-agenda-change-all-lines)
(org-agenda-add-entry-to-org-agenda-diary-file): Rename
`org-format-agenda-item' to `org-agenda-format-item'.
Using the `org-agenda-' prefix makes more sense here.