avoid the 'target' buffer in dns_name_fromtext()

avoid the 'target' buffer in dns_name_fromtext()

dns_name_fromtext() stores the converted name in the 'name'
passed to it, and optionally also copies it in wire format to
a buffer 'target'. this makes the interface unnecessarily
complex, and could be simplified by having a different function
for each purpose. as a first step, remove uses of the target
buffer in calls to dns_name_fromtext() where it wasn't actually
needed.