Removed default value sccpregistration for regcontext. When regcontext is not available in sccp.conf the entries are not created. BTW regcontext is only used for dundi lookup purposes

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@4156 43c1dc8c-776e-4df2-8ef1-6e829299be21