GUACAMOLE-408: don't try to clean up the local Maven repository

There's no need to clean up the local Maven repository after the
build, since only the artifacts we want are copied to the runtime
image. For reasons not investigated, attempting to remove the
local repository directory fails because the directory is in use
after the build.

guacamole-docker/bin/build-guacamole.sh

@@ -54,7 +54,6 @@ mkdir -p "$DESTINATION"
 
 cd "$BUILD_DIR"
 mvn package
-rm -Rf ~/.m2
 
 #
 # Copy guacamole.war to destination