Document dropped options from icinga.cfg in Icinga 1.10

The option 'log_external_commands_user' in icinga.cfg was deprecated since Icinga version 1.7 (see issue #1619).
The option 'event_profiling_enabled' in icinga.cfg was deprecated since Icinga version 1.9 (see issue #4054).

Both options have been dropped in Icinga version 1.10. This patch documents the dropped options.

Cross reference log_external_commands_user: commit b09982c90fb38045e606daec1805aeb163884832.
Cross reference event_profiling_enabled: commit 65876dfc4627cb4fea198f8282a08a334f35cb14.

Signed-off-by: Michael Friedrich <Michael.Friedrich@netways.de>

Fixes #4957