Fix leak in gss_display_name() for non-MN names

Fix leak in gss_display_name() for non-MN names

RFC 2744 states that the gss_display_name() output_name_type result is
"a pointer into static storage, and should be treated as read-only by
the caller (in particular, the application should not attempt to free
it)".  For non-mechanism names, we were making a copy of the name type
from the union name structure, causing a memory leak; stop doing that.

ticket: 8439 (new)
target_version: 1.14-next
target_version: 1.13-next
tags: pullup