Akuli and srittau: Remove Python 2 branches from Python 3 stubs (#5461)

* run script and do some manual changes (Akuli)

* do the whole thing manually (srittau)

* merge changes (Akuli)

Co-authored-by: Sebastian Rittau <srittau@rittau.biz>

stdlib/lib2to3/pgen2/token.pyi

@@ -1,4 +1,3 @@
-import sys
 from typing import Dict, Text
 
 ENDMARKER: int
@@ -54,13 +53,11 @@ DOUBLESLASHEQUAL: int
 OP: int
 COMMENT: int
 NL: int
-if sys.version_info >= (3,):
-    RARROW: int
-if sys.version_info >= (3, 5):
-    AT: int
-    ATEQUAL: int
-    AWAIT: int
-    ASYNC: int
+RARROW: int
+AT: int
+ATEQUAL: int
+AWAIT: int
+ASYNC: int
 ERRORTOKEN: int
 N_TOKENS: int
 NT_OFFSET: int