remove duplicated methane from test cases

Author: SalvadorBrandolin

tests/cases/particulars.py

@@ -409,15 +409,6 @@
         joback_result={"=C=": 1, "=O (other than above)": 2},
         dortmund_result={},
     ),
-    Case(
-        identifier="C",
-        identifier_type="smiles",
-        cases_module="particulars",
-        unifac_result={},
-        psrk_result={"CH4": 1},
-        joback_result={},
-        dortmund_result={},
-    ),
     Case(
         identifier="O=O",
         identifier_type="smiles",