Actions:
* Move get_ns_count(), get_tick_count(), and get_gmt_time() from misc_os_dependent.h to time_helper.h. I did this because all those functions are time-related and under the same namespace
* Remove misc_os_dependent.h because it is now empty
* Change all includes of misc_os_dependent.h to time_helper.h where appropriate
* Remove get_time_string*() from time_helper.h b/c its unused
* Remove get_time_t_from_ole_date() from time_helper.h b/c its unused
* Remove odbc_time_to_oledb_taime() from time_helper.h b/c its unused
* Refactor get_ns_count() to use std::chrono instead of 4 different implementation-specific hacks
9a59b131c4