keycloak/deposit: Drop option direct_grant_flow
keycloak/deposit: Drop option direct_grant_flow

With this option, flaky connections happen with unknown-error keycloak server side.
Without it, connection happens without issues.

Related to P985
Related to T3171#61488

SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site