[ReadHandler] Remove timing related flags

[lpbeliveau-silabs]

Mentionned here: https://github.com/project-chip/connectedhomeip/pull/28104/files#r1269742928

TestReadInteraction relies on flags to simulate expiration of ReadHandler timers, they have been migrated to the ReadHandlerNode object of the ReportScheduler and additionnal test code was ifdefed in to allow those flags to work as they were originally implemented.

We need to remove all code in the #ifdef CONFIG_BUILD_FOR_HOST_UNIT_TEST and modify our test to stop relying on the flags.

Easiest way would be to have the test wait for the timers to elapse but that would slow down a test that is already slow.

Other options would be: modify the timestamps to be <= now and ensure to call the appropriate callbacks if expiration is supposed to have happen, manually bump up the timestamp, change the concept of "now" in checks for reportability.

[lpbeliveau-silabs]

Will help reduce ram usage for : #28277