workflows: Remove the ARCH=arm bcm2711 build

As we will be moving Pi 4 support to kernel8.img only and dropping
kernel7l.img, the ARCH=arm bcm2711 defconfig has been deleted.
Remove the corresponding autobuild.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

Author: pelwell

.github/workflows/kernel-build.yml

@@ -41,11 +41,6 @@ jobs:
             kernel: kernel7
 
           - name: bcm2711
-            arch: arm
-            defconfig: bcm2711_defconfig
-            kernel: kernel7l
-
-          - name: bcm2711_arm64
             arch: arm64
             defconfig: bcm2711_defconfig
             kernel: kernel8