Revert "[red-knot] Type narrowing for assertions (#17149)" (#17335)

I merged #17149 without checking the ecosystem results, and it still
caused a cycle panic in pybind11. Reverting for now until I fix that, so
we don't lose the ecosystem signal on other PRs.

crates/red_knot_python_semantic/resources/mdtest/narrow/assert.md

@@ -1,53 +0,0 @@
-# Narrowing with assert statements
-
-## `assert` a value `is None` or `is not None`
-
-```py
-def _(x: str | None, y: str | None):
-    assert x is not None
-    reveal_type(x)  # revealed: str
-    assert y is None
-    reveal_type(y)  # revealed: None
-```
-
-## `assert` a value is truthy or falsy
-
-```py
-def _(x: bool, y: bool):
-    assert x
-    reveal_type(x)  # revealed: Literal[True]
-    assert not y
-    reveal_type(y)  # revealed: Literal[False]
-```
-
-## `assert` with `is` and `==` for literals
-
-```py
-from typing import Literal
-
-def _(x: Literal[1, 2, 3], y: Literal[1, 2, 3]):
-    assert x is 2
-    reveal_type(x)  # revealed: Literal[2]
-    assert y == 2
-    reveal_type(y)  # revealed: Literal[1, 2, 3]
-```
-
-## `assert` with `isinstance`
-
-```py
-def _(x: int | str):
-    assert isinstance(x, int)
-    reveal_type(x)  # revealed: int
-```
-
-## `assert` a value `in` a tuple
-
-```py
-from typing import Literal
-
-def _(x: Literal[1, 2, 3], y: Literal[1, 2, 3]):
-    assert x in (1, 2)
-    reveal_type(x)  # revealed: Literal[1, 2]
-    assert y not in (1, 2)
-    reveal_type(y)  # revealed: Literal[3]
-```