Why do we have this? It means warnings aren't filtered in acme tests (#10267)

This was added in https://github.com/certbot/certbot/pull/6091 to make
tests pass in EPEL and older ubuntus, 7 years ago. It is probably no
longer needed.

| pytest version | min. Python version |
|---------------|---------------------|
|8.0+ | 3.8+|
| 7.1+ | 3.7+ |
| 6.2 - 7.0 | 3.6+ |
| 5.0 - 6.1 | 3.5+ |
| 3.3 - 4.6 | 2.7, 3.4+ |

That version is [no longer
supported](https://docs.pytest.org/en/stable/backwards-compatibility.html).

Probably therefore we can just get rid of this.

acme/MANIFEST.in

@@ -1,6 +1,5 @@
 include LICENSE.txt
 include README.rst
-include pytest.ini
 recursive-include docs *
 recursive-include examples *
 recursive-include src/acme/_internal/tests/testdata *

acme/pytest.ini

@@ -1,2 +0,0 @@
-[pytest]
-norecursedirs = .* build dist CVS _darcs {arch} *.egg