Drop Raspberry Pi 1/Zero W support (#1638)

These boards support the rather ancient ARMv6 architecture only. We
officially stopped supporting them already two releases ago, its time to
say goodbye.

.github/workflows/matrix.json

@@ -41,18 +41,6 @@
     "runner": "aarch64-runner",
     "label": "board/odroid"
   },
-  {
-    "id": "rpi",
-    "defconfig": "rpi",
-    "runner": "arm-runner",
-    "label": "board/raspberrypi"
-  },
-  {
-    "id": "rpi0-w",
-    "defconfig": "rpi0_w",
-    "runner": "arm-runner",
-    "label": "board/raspberrypi"
-  },
   {
     "id": "rpi2",
     "defconfig": "rpi2",