py/qstrdefs: Remove unused qstrs.

They are not used by any component and take up valuable flash space.

py/qstrdefs.h

@@ -51,11 +51,3 @@ Q(<genexpr>)
 Q(<string>)
 Q(<stdin>)
 Q(utf-8)
-
-// The following qstrings not referenced from anywhere in the sources
-Q(__locals__)
-Q(BufferError)
-Q(FileExistsError)
-Q(FileNotFoundError)
-Q(FloatingPointError)
-Q(UnboundLocalError)