lib: remove libtool version for iOS/tvOS

The libtool versionning is there to handle linkage compatibility during
runtime with older/more recent version of the libraries. On iOS and
tvOS, the dynamic libraries MUST be shipped in a framework. A framework
already provides its own way of handling versionning, and applications
cannot install global dynamic libraries (except maybe on jailbroken
devices) so cannot really use the libtool versionning features for
anything.