[release] Bump version 3.0.0-rc1

batsim/_version.py

-__version__ = "3.0.0-alpha"
+__version__ = "3.0.0-rc1"

setup.py

@@ -145,7 +145,6 @@ setup(
     zip_safe=False,
     description="Python scheduler for Batsim",
     long_description=read_me,
-    long_description_content_type='text/markdown',
     keywords='Scheduler',
     license='LGPLv3',
     classifiers=[