[202405][FC] remove FC delay field

[stepanblyschak]

What I did

Simplify approach to delaying counters on warm boot and fast boot. Removed FLEX_COUNTER_DELAY_STATUS_FIELD and instead postpone all FC processing to happen after apply view to not delay data plane configuration.

The CONFIG_DB should not be updated in runtime anymore for counters to be delayed.

How I did it

Removed FLEX_COUNTER_DELAY_STATUS_FIELD and corresponding counterpoll commands (that weren't supposed to be used by user directly anyway). Updated db_migrator.py to remove that field.

How to verify it

Ran fast-reboot from 202405. Made sure no delay field present, counters are enabled and delayed.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)