Simplify and correct many numeric unions (#7906)

Unblocks PyCQA/flake8-pyi#222

stubs/typed-ast/typed_ast/ast27.pyi

@@ -237,7 +237,7 @@ class Repr(expr):
     value: expr
 
 class Num(expr):
-    n: int | float | complex
+    n: complex
 
 class Str(expr):
     s: str | bytes

stubs/typed-ast/typed_ast/ast3.pyi

@@ -252,7 +252,7 @@ class Call(expr):
     keywords: list[keyword]
 
 class Num(expr):
-    n: float | int | complex
+    n: complex
 
 class Str(expr):
     s: str