Man pages matching name gnutls_db_set_remove_function in section 3:

gnutls_db_set_remove_function.3.en	debian 10 / gnutls-doc
gnutls_db_set_remove_function.3.en	debian 11 / gnutls-doc
gnutls_db_set_remove_function.3.en	debian 12 / gnutls-doc