s3: Remove debug_ctx()

s3: Remove debug_ctx()

smbd just crashed on me: In a debug message I called a routine preparing a
string that itself used debug_ctx. The outer routine also used it after the
inner routine had returned. It was still referencing the talloc context
that the outer debug_ctx() had given us, which the inner DEBUG had already
freed.
(cherry picked from commit 172542036aa1047cc7ee95c8e0a33dead6b3076f)