COMP: Disable OpenSSL support by default

This commit ensures the OpenSSL support is disabled by default as claimed
within the commit message associated to r22220.

Discussion: http://slicer-devel.65872.n3.nabble.com/Windows-build-fails-due-to-missing-QSslSocket-class-tt4029446.html#a4029460

Thanks Greg Sharp for reporting the issue.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22228 3bd1e089-480b-0410-8dfb-8563597acbee