kernel-install: strip BOOT_IMAGE= from kernel options

https://bugzilla.redhat.com/show_bug.cgi?id=1716164.

src/kernel-install/90-loaderentry.install

@@ -55,6 +55,7 @@ else
     read -r -d '' -a line < /proc/cmdline
     for i in "${line[@]}"; do
         [[ "${i#initrd=*}" != "$i" ]] && continue
+        [[ "${i#BOOT_IMAGE=*}" != "$i" ]] && continue
         BOOT_OPTIONS+=("$i")
     done
 fi