Update setup.py to install dl1_data_handler from pypi

When creating a new env with gammalearn to be installed from pip, I get the following error:

Pip subprocess error:
ERROR: Packages installed from PyPI cannot depend on packages which are not also hosted on PyPI.
gammalearn depends on dl1_data_handler@ https://github.com/cta-observatory/dl1-data-handler/archive/v0.10.0.zip

dl1_data_handler is now on pypi, so this should fix the issue.