ENH: remove moto from requirements-dev.txt
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Hi
There seems to be no code in the source code that uses "moto". But in “requirements-dev.txt”, "moto" is still listed as a dependency.
The following commit removed "import moto" in "pandas/tests/io/conftest.py ".
[TST: make it possible to run tests without moto installed ](https://github.com/pandas-dev/pandas/commit/c753e1e08b01a438aaa252327de046109bf4bcfd)
So should it be removed from "requirements-dev.txt"?

