Move plymouth theme setting to kali-themes

We divert plymouth's configuration file to install our version
configuring the kali theme. Stop using the plymouth-set-default-theme
in kali-desktop-base.

debian/kali-desktop-base.postinst

@@ -104,17 +104,6 @@ if [ "$1" = "configure" ] || [ "$1" = "abort-upgrade" ] || [ "$1" = "abort-remov
 
 fi
 
-# Set Kali as default plymouth theme (on initial install and upgrade from
-# old version)
-if [ "${1}" = "configure" ] && dpkg --compare-versions "$2" lt "2019.4.0"; then
-    if which plymouth-set-default-theme > /dev/null; then
-        plymouth-set-default-theme kali
-	if which update-initramfs > /dev/null; then
-	    update-initramfs -u
-        fi
-    fi
-fi
-
 desktop_base_version=$(dpkg-query -f'${Version}' -W desktop-base 2>/dev/null || true)
 if [ "$1" = "configure" ]; then
     if dpkg --compare-versions "$desktop_base_version" lt-nl 10.0.3+kali3 || \