Drop support for EOL Ubuntu 21.04 (#11961)

changelog.d/11961.removal

@@ -0,0 +1 @@
+No longer build `.deb` packages for Ubuntu 21.04 Hirsute Hippo, which has now EOLed.

scripts-dev/build_debian_packages

@@ -25,7 +25,6 @@ DISTS = (
     "debian:bookworm",
     "debian:sid",
     "ubuntu:focal",  # 20.04 LTS (our EOL forced by Py38 on 2024-10-14)
-    "ubuntu:hirsute",  # 21.04 (EOL 2022-01-05)
     "ubuntu:impish",  # 21.10  (EOL 2022-07)
 )