Replace AJAX by search in 'mwsuggest-disable'

AJAX is jargon that is most probbly not understood by the average user.
Brought up by Tgr in
https://translatewiki.net/wiki/Thread:Support/MediaWiki:Mwsuggest-disable_is_too_technical

Change-Id: I736d0c16dab50b3e313652c3b9b2680fa104ad32