SOLR-5604 is the issue where I talk about deprecations in HC.
I have already tried the HttpClient 4.4 upgrade in Solr without any new test failures, and I'm using HC 4.4 in my own SolrJ code, so I know they have not removed the deprecated methods. I am confident that HC uses the same deprecation policy that we do, which indicates that the deprecated code will not be removed until HC 5.0.
As I indicated on
SOLR-5604, It looks like HC is slowly gearing up for a 5.0-alpha release, though I cannot tell how quickly those plans are proceeding. Perhaps Oleg Kalnichevski can fill in the blanks.