(def-gdb-auto-updated-buffer)

(def-gdb-auto-updated-buffer)
(def-gdb-auto-update-trigger): Simplify construction.
(gdb-locals-buffer): Use def-gdb-auto-update-trigger instead of
def-gdb-auto-updated-buffer as gdb-info-locals-handler is
defined explicitly.
(gdb-assembler-buffer): Use def-gdb-auto-update-handler instead of
def-gdb-auto-updated-buffer as gdb-invalidate-assembler is
defined explicitly.
(gdb-info-locals-custom): Remove as it's a no-op.