Feature: libpe_status,libpe_rules: drop support for default-action-timeout

... deprecated operation meta-attribute, along with its alias
default_action_timeout. Also, update affected documentation and regression
tests.

This results in one change in behavior: if no timeout is explicitly configured,
whether in operation XML or in op_defaults, then the usual hardcoded default of
20 seconds will be used. Due to some unknown bug, it would previously use 40
seconds in this situation.