clean python 3 specific stuff from stdlib/@python2 stubs (#5451)

stdlib/@python2/linecache.pyi

@@ -8,6 +8,3 @@ def clearcache() -> None: ...
 def getlines(filename: Text, module_globals: Optional[_ModuleGlobals] = ...) -> List[str]: ...
 def checkcache(filename: Optional[Text] = ...) -> None: ...
 def updatecache(filename: Text, module_globals: Optional[_ModuleGlobals] = ...) -> List[str]: ...
-
-if sys.version_info >= (3, 5):
-    def lazycache(filename: Text, module_globals: _ModuleGlobals) -> bool: ...