In `wp_xmlrpc_server` methods, for comprehensibility:

* initialize arrays in loops, instead of overriding an uninitialized array each time
* in `->blogger_getRecentPosts()` and `->mw_getRecentPosts()`, remove the extra loops by only setting one `array`

See #30224.


git-svn-id: https://develop.svn.wordpress.org/trunk@30153 602fd350-edb4-49c9-b593-d223f7449a82