lib/db: remove deprecated implementation of db_get_login() and replace it with that of db_get_login2()
db_get_login() is deprecated in 7.8.0 release with da399c52637ee5c81228459fa374a114c8fef06c. Change its function signature and implementation to match that of the currently preferred db_get_login2().
Modify db_get_login2() to internally call db_get_login() function call. In the future major version, db_get_login2() would be removed to have only one method to get login details for simplicity.
db_get_login() was deprecated (in favour of db_get_login2()) in 2015 with the 7.8.0 release: https://github.com/OSGeo/grass/commit/da399c52637ee5c81228459fa374a114c8fef06c
I think this (8.5) may the moment to drop it.
(The CodeQL CI failure is unrelated to changes of this PR.)