util/docker/coreboot-sdk: Remove doxygen

Doxygen was removed at the project level.  Remove the doxygen Debian
package and make target.

Change-Id: Ib82ba7890e7f53357eeca318b5f844164747aecd
Signed-off-by: Tom Hiller <thrilleratplay@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67039
Reviewed-by: Felix Singer <felixsinger@posteo.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/docker/coreboot-sdk/Dockerfile

@@ -29,7 +29,6 @@ RUN \
 		device-tree-compiler \
 		dh-autoreconf \
 		diffutils \
-		doxygen \
 		exuberant-ctags \
 		flex \
 		g++ \
@@ -135,10 +134,6 @@ RUN \
   make -C coreboot ctags-project && \
   make -C coreboot cscope-project
 
-RUN \
-  cd /tmp/work && \
-  make -C coreboot doxygen -j
-
 RUN \
   cd /tmp/work && \
   make -C coreboot test-payloads&& \