Check statements that are no-op for reachability

[hauntsaninja]

python/typing#1671

The narrowed types here are maybe a little sketchy / not sure how valuable this is

[github-actions]

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

aioredis (https://github.com/aio-libs/aioredis)
+ aioredis/client.py:4288: error: If x = b'abc' then f"{x}" or "{}".format(x) produces "b'abc'", not "abc". If this is desired behavior, use f"{x!r}" or "{!r}".format(x). Otherwise, decode the bytes  [str-bytes-safe]
+ aioredis/client.py:4291: error: If x = b'abc' then f"{x}" or "{}".format(x) produces "b'abc'", not "abc". If this is desired behavior, use f"{x!r}" or "{!r}".format(x). Otherwise, decode the bytes  [str-bytes-safe]

streamlit (https://github.com/streamlit/streamlit)
+ lib/streamlit/type_util.py: note: In function "to_bytes":
+ lib/streamlit/type_util.py:164:26: error: If x = b'abc' then f"{x}" or "{}".format(x) produces "b'abc'", not "abc". If this is desired behavior, use f"{x!r}" or "{!r}".format(x). Otherwise, decode the bytes  [str-bytes-safe]

core (https://github.com/home-assistant/core)
+ homeassistant/helpers/template.py:719: error: Value of type "None" is not indexable  [index]