When checking for previous new_blog_post entries to prevent bumping, skip the author ID check

The author ID check is superfluous - post_id and blog_id is sufficient to
identify a unique activity item corresponding to a specific post. Moreover, the
additional check breaks the intended functionality when the post is edited to
have a new author.

Fixes #4806

Props czarate

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7169 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Pinking shears

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7170 cdf35c40-ae34-48e0-9cc9-0c9da1808c22