SproutForms Problem Getting Update Feed
These two items are unrelated.

First, there's no need to worry about the deprecation errors.  We actively maintain our plugins and will have them resolved before they should have any effect on general use of our plugins. We've made a feature request to Craft to consider to reduce the prominence of the deprecation message, as it generally just causes unneeded alarm.

Second, the releases message is probably due to us currently having an SNI SSL certificate installed and some older server configurations choke because they don't know how to deal with them. The error probably indicates that you may be running fairly old software on your server.

If you're curious, I was told by Craft support:


  Technically there are 3 things a server needs for it to be able to
  recognize SNI SSL certs.
  
  1) Using a version of cURL that supports it, at least 7.18.1 (8 years
  old: https://curl.haxx.se/changes.html)
  
  2) Using a version of cURL compiled against a library that supports
  SNI, e.g. OpenSSL 0.9.8j (depending on the compilation options some
  older versions. 7 years old:
  https://www.openssl.org/news/changelog.html)
  
  3) Using TLS 1.0 at least (not SSLv3)