chore: remove repetitive words

Signed-off-by: majorteach <csgcgl@126.com>

slither/core/declarations/contract.py

@@ -894,7 +894,7 @@ class Contract(SourceMapping):  # pylint: disable=too-many-public-methods
 
     def get_function_from_canonical_name(self, canonical_name: str) -> Optional["Function"]:
         """
-            Return a function from a a canonical name (contract.signature())
+            Return a function from a canonical name (contract.signature())
         Args:
             canonical_name (str): canonical name of the function (without return statement)
         Returns:

slither/vyper_parsing/declarations/function.py

@@ -554,7 +554,7 @@ class FunctionVyper:  # pylint: disable=too-many-instance-attributes
     def _parse_returns(self, returns: Union[Name, TupleVyper, Subscript]):
 
         self._function.returns_src().set_offset(returns.src, self._function.compilation_unit)
-        # Only the type of the arg is given, not a name. We create an an `Arg` with an empty name
+        # Only the type of the arg is given, not a name. We create an `Arg` with an empty name
         # so that the function has the correct return type in its signature but doesn't clash with
         # other identifiers during name resolution (`find_variable`).
         if isinstance(returns, (Name, Subscript)):