Minor post 0.3.0 bug fixes for data release 1.0.0

Two very minor issues found after the 0.3.0 release, but before the
first data release...
* Failed to specify upper bound on Python version in setup.py
* Inappropriately checking for original source data in the
  epacems_to_parquet conversion script -- when the script uses the
  datapackage, not the original data in the datastore.

setup.py

@@ -81,8 +81,7 @@
         'electricity', 'energy', 'data', 'analysis', 'mcoe', 'climate change',
         'finance', 'eia 923', 'eia 860', 'ferc', 'form 1', 'epa ampd',
         'epa cems', 'coal', 'natural gas', ],
-    # python_requires='>=3.7, <3.8.0a0',
-    python_requires='>=3.7',
+    python_requires='>=3.7, <3.8.0a0',
     setup_requires=['setuptools_scm'],
     install_requires=install_requires,
     extras_require={

src/pudl/convert/epacems_to_parquet.py

@@ -314,18 +314,6 @@ def main():
     pudl_settings = pudl.workspace.setup.derive_paths(
         pudl_in=args.pudl_in, pudl_out=args.pudl_out)
 
-    # Make sure the required input files are available before we go doing a
-    # bunch of work cloning the database...
-    logger.info("Checking for required EPA CEMS input files...")
-    pudl.helpers.verify_input_files(
-        ferc1_years=[],
-        eia860_years=[],
-        eia923_years=[],
-        epacems_years=args.years,
-        epacems_states=args.states,
-        pudl_settings=pudl_settings,
-    )
-
     epacems_to_parquet(datapkg_path=pathlib.Path(args.datapkg),
                        epacems_years=args.years,
                        epacems_states=args.states,

src/pudl/glue/ferc1_eia.py

@@ -343,9 +343,8 @@ def get_db_plants_eia(pudl_engine):
             engine for connecting to a PUDL SQLite database.
 
     Returns:
-        :class:`pandas.DataFrame`: A DataFrame with plant_id_eia,
-        plant_name_eia, and state columns, for addition to the FERC 1 / EIA
-        plant mappings.
+        pandas.DataFrame: A DataFrame with plant_id_eia, plant_name_eia, and
+        state columns, for addition to the FERC 1 / EIA plant mappings.
 
     """
     db_plants_eia = (
@@ -370,7 +369,7 @@ def get_mapped_plants_eia():
         None
 
     Returns:
-        :class:`pandas.DataFrame`: A DataFrame listing the plant_id_eia and
+        pandas.DataFrame: A DataFrame listing the plant_id_eia and
         plant_name_eia values for every EIA plant which has already been
         assigned a PUDL Plant ID.