Revert use of recursive alias in typeshed

[hauntsaninja]

Easy crash to repro: mypy --any-exprs-report=out -c 'pass' --show-traceback

[hauntsaninja]

  File "/Users/shantanu/dev/mypy/mypy/type_visitor.py", line 409, in visit_type_alias_type
    return get_proper_type(t).accept(self)
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 1791, in accept
    return visitor.visit_callable_type(self)
  File "/Users/shantanu/dev/mypy/mypy/type_visitor.py", line 374, in visit_callable_type
    return self.query_types(t.arg_types + [t.ret_type])
  File "/Users/shantanu/dev/mypy/mypy/typeanal.py", line 1934, in query_types
    return self.strategy([t.accept(self) for t in types]) + list(types)
  File "/Users/shantanu/dev/mypy/mypy/typeanal.py", line 1934, in <listcomp>
    return self.strategy([t.accept(self) for t in types]) + list(types)
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 2594, in accept
    return visitor.visit_union_type(self)
  File "/Users/shantanu/dev/mypy/mypy/type_visitor.py", line 392, in visit_union_type
    return self.query_types(t.items)
  File "/Users/shantanu/dev/mypy/mypy/typeanal.py", line 1934, in query_types
    return self.strategy([t.accept(self) for t in types]) + list(types)
  File "/Users/shantanu/dev/mypy/mypy/typeanal.py", line 1934, in <listcomp>
    return self.strategy([t.accept(self) for t in types]) + list(types)
  File "/Users/shantanu/dev/mypy/mypy/types.py", line 321, in accept
    return visitor.visit_type_alias_type(self)
...
RecursionError

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

discord.py (https://github.com/HitSyr/discord.py)
- discord/ext/commands/converter.py:1177: error: Argument 2 to "issubclass" has incompatible type "<typing special form>"; expected "_ClassInfo"  [arg-type]
+ discord/ext/commands/converter.py:1177: error: Argument 2 to "issubclass" has incompatible type "<typing special form>"; expected "Union[type, UnionType, Tuple[Union[type, UnionType, Tuple[Any, ...]], ...]]"  [arg-type]
- discord/ext/commands/hybrid.py:206: error: Argument 2 to "isinstance" has incompatible type "_SpecialForm"; expected "_ClassInfo"  [arg-type]
+ discord/ext/commands/hybrid.py:206: error: Argument 2 to "isinstance" has incompatible type "_SpecialForm"; expected "Union[type, UnionType, Tuple[Union[type, UnionType, Tuple[Any, ...]], ...]]"  [arg-type]

[ilevkivskyi]

@hauntsaninja I hope #14136 should help with this.