Fix and enable simplifiable-if-statement lint

.pylintrc

@@ -29,8 +29,7 @@
 #TODO: Enable too-many-return-statements
 #TODO: Enable too-many-nested-blocks
 #TODO: Enable super-init-not-called
-#TODO: Enable simplifiable-if-statement
 #TODO: Enable no-self-use
 #TODO: Enable no-member
 
-disable=missing-docstring,too-few-public-methods,too-many-arguments,no-init,duplicate-code,invalid-name,suppressed-message,locally-disabled,protected-access,no-name-in-module,unused-argument,fixme,wrong-import-order,no-value-for-parameter,cyclic-import,unused-variable,redefined-outer-name,unused-import,too-many-instance-attributes,broad-except,too-many-locals,too-many-lines,redefined-variable-type,next-method-called,import-error,useless-else-on-loop,too-many-return-statements,too-many-nested-blocks,super-init-not-called,simplifiable-if-statement,no-self-use,no-member
+disable=missing-docstring,too-few-public-methods,too-many-arguments,no-init,duplicate-code,invalid-name,suppressed-message,locally-disabled,protected-access,no-name-in-module,unused-argument,fixme,wrong-import-order,no-value-for-parameter,cyclic-import,unused-variable,redefined-outer-name,unused-import,too-many-instance-attributes,broad-except,too-many-locals,too-many-lines,redefined-variable-type,next-method-called,import-error,useless-else-on-loop,too-many-return-statements,too-many-nested-blocks,super-init-not-called,no-self-use,no-member

src/python/grpcio/grpc/_auth.py

@@ -48,11 +48,8 @@ class GoogleCallCredentials(grpc.AuthMetadataPlugin):
 
         # Hack to determine if these are JWT creds and we need to pass
         # additional_claims when getting a token
-        if 'additional_claims' in inspect.getargspec(
-                credentials.get_access_token).args:
-            self._is_jwt = True
-        else:
-            self._is_jwt = False
+        self._is_jwt = 'additional_claims' in inspect.getargspec(
+            credentials.get_access_token).args
 
     def __call__(self, context, callback):
         # MetadataPlugins cannot block (see grpc.beta.interfaces.py)