Remove redundant post ID validation.

Props SergeyBiryukov
fixes #24199


git-svn-id: http://core.svn.wordpress.org/trunk@24249 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add default args list to wp_remote_request|get|post|head docblocks

Props DrewAPicture
fixes #23838


git-svn-id: http://core.svn.wordpress.org/trunk@24250 1a063a9b-81f0-0310-95a4-ce76da25c4cd