[wip/pal-hardware-gazebo-melodic] Simplifies Makefile

This package is Ubuntu-18-04-LTS only, thus there is no
need to test the package for the dependency.

pal-hardware-gazebo-melodic/Makefile

@@ -10,6 +10,7 @@ DISTNAME=	${VERSION}
 ROSNAME=	$(subst -,_,${PRFNAME})
 WRKSRC=		${WRKDIR}/${ROSNAME}-${VERSION}
 DIST_SUBDIR=	${PKGBASE}
+PKGREVISION=	1
 
 CATEGORIES=	wip
 
@@ -39,14 +40,7 @@ include ../../lang/ros-message-runtime/depend.mk
 include ../../middleware/ros-comm/depend.mk
 include ../../wip/pal-hardware-interfaces/depend.mk
 include ../../wip/pal-statistics/depend.mk
-
-include ../../wip/sysdep/ubuntu-distro.mk
-ifeq (bionic,${UBUNTUDISTRO})
-  include ../../wip/prf-gazebo-ros-pkgs-melodic/depend.mk
-else
-  include ../../wip/prf-gazebo-ros-pkgs/depend.mk
-endif
-
+include ../../wip/prf-gazebo-ros-pkgs-melodic/depend.mk
 include ../../wip/prf-ros-control/depend.mk
 include ../../wip/dynamic-introspection/depend.mk
 include ../../motion/ros-control-toolbox/depend.mk