Drop osc-setup, rely on OSC_CONFIG being set

The pkg group now sets the OSC_CONFIG environment variable in its CI settings to provide the whole configuration for the connection to OBS, removing the need for the osc-setup script to take the OSC_USERNAME and OSC_PASSWORD variables and put them in ~/.oscrc.

The CI/CD settings of the tests/dash> project used by the test pipeline have already been updated to drop OSC_USERNAME and OSC_PASSWORD while introducing OSC_CONFIG.