Coverage: Removed unreachable code from heat engine

While looking for coverage metrics found unreachable code
Fixing the same in this commit

Change-Id: I1265057af4a91accff92f378e9e1f353d77813c6

heat/engine/parameters.py

@@ -170,8 +170,6 @@ class Schema(constr.Schema):
         else:
             return super(Schema, self).__getitem__(key)
 
-        raise KeyError(key)
-
 
 class Parameter(object):
     '''A template parameter.'''

heat/engine/properties.py

@@ -193,8 +193,6 @@ class Schema(constr.Schema):
         else:
             return super(Schema, self).__getitem__(key)
 
-        raise KeyError(key)
-
 
 def schemata(schema_dicts):
     """