simplify

Author: yaacovCR

spec/Section 6 -- Execution.md

@@ -738,18 +738,9 @@ ResolveAbstractType(abstractType, objectValue):
   the type system for determining the Object type of {abstractType} given the
   value {objectValue}.
 - Assert {resolvedType} is an Object type.
-- Assert {IsSubType(abstractType, resolvedType)}.
+- Assert {resolvedType} implements {abstractType}.
 - Return {resolvedType}.
 
-IsSubType(superType, maybeSubType):
-
-- If {abstractType} is an Interface type.
-  - If {resolvedType} implements {abstractType}, return {true}.
-  - Otherwise, return {false}.
-- If {abstractType} is a Union type.
-  - If {resolvedType} is a member type of {abstractType}, return {true}.
-  - Otherwise, return {false}.
-
 **Merging Selection Sets**
 
 When more than one field of the same name is executed in parallel, their