refactor: remove deprecated `system/bootstrap.php` #14324

Job	Run time
Setup PHP Version for Code Coverage	3s
Others (8.5) / Sanity Tests	2m 33s
Others (8.3) / Sanity Tests	2m 37s
Others (8.4) / Sanity Tests	2m 44s
Others (8.2) / Sanity Tests	3m 35s
CacheLive (8.5) / Cache Live Tests	2m 5s
CacheLive (8.3) / Cache Live Tests	2m 11s
SeparateProcess (8.3) / tests	3m 24s
SeparateProcess (8.5) / tests	3m 35s
DatabaseLive (8.3, SQLite3, 8.0) / tests	2m 29s
CacheLive (8.4) / Cache Live Tests	2m 7s
CacheLive (8.2) / Cache Live Tests	2m 21s
DatabaseLive (8.4, SQLite3, 8.0) / tests	2m 16s
SeparateProcess (8.4) / tests	3m 3s
DatabaseLive (8.4, SQLSRV, 8.0) / tests	5m 31s
DatabaseLive (8.4, MySQLi, 8.0) / tests	5m 47s
DatabaseLive (8.5, OCI8, 8.0) / tests	6m 53s
DatabaseLive (8.3, OCI8, 8.0) / tests	7m 5s
DatabaseLive (8.3, Postgre, 8.0) / tests	3m 10s
DatabaseLive (8.4, Postgre, 8.0) / tests	2m 51s
DatabaseLive (8.3, MySQLi, 8.0) / tests	4m 54s
DatabaseLive (8.5, Postgre, 8.0) / tests	2m 50s
DatabaseLive (8.2, MySQLi, 8.0) / tests	4m 48s
DatabaseLive (8.2, SQLite3, 8.0) / tests	3m 3s
SeparateProcess (8.2) / tests	3m 29s
DatabaseLive (8.5, SQLite3, 8.0) / tests	2m 16s
DatabaseLive (8.5, MySQLi, 8.0) / tests	4m 3s
DatabaseLive (8.2, OCI8, 8.0) / tests	7m 40s
DatabaseLive (8.3, SQLSRV, 8.0) / tests	5m 28s
DatabaseLive (8.2, SQLSRV, 8.0) / tests	6m 39s
DatabaseLive (8.2, MySQLi, 5.7) / tests	4m 36s
DatabaseLive (8.4, OCI8, 8.0) / tests	7m 18s
DatabaseLive (8.5, SQLSRV, 8.0) / tests	5m 21s
DatabaseLive (8.2, Postgre, 8.0) / tests	3m 26s
Upload coverage results to Coveralls / coveralls	39s
	2h 12m 50s

Provide feedback