Removal of libgc detection/infrastructure (Not used anyway)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5256 43c1dc8c-776e-4df2-8ef1-6e829299be21
Possible fix for sccp_channel_end_forwarding_channel when used during autoanswer (Reported by Stefan Gofferje: Requires renewed test)

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5258 43c1dc8c-776e-4df2-8ef1-6e829299be21