makefiles: include config.mk instead of common.mk where possible

common.mk contains definitions for building programs and it includes
config.mk.

Some makefiles that include common.mk do not contain any targets for
building programs.  They depend only on configure-time variable
definitions (which are defined on config.mk) rather than anything
specific to common.mk.  So change their includes of common.mk to
config.mk.

src/bash_completion/Makefile.in

@@ -2,7 +2,7 @@
 all: firejail.bash_completion
 
 ROOT = ../..
-include $(ROOT)/src/common.mk
+include $(ROOT)/config.mk
 
 firejail.bash_completion: firejail.bash_completion.in
  gawk -f ../man/preproc.awk -- $(MANFLAGS) < $< > $@.tmp

src/man/Makefile.in

@@ -2,7 +2,7 @@
 all: firecfg.man firejail.man firejail-login.man firejail-users.man firejail-profile.man firemon.man jailcheck.man
 
 ROOT = ../..
-include $(ROOT)/src/common.mk
+include $(ROOT)/config.mk
 
 %.man: %.txt
  gawk -f ./preproc.awk -- $(MANFLAGS) < $< > $@

src/zsh_completion/Makefile.in

@@ -2,7 +2,7 @@
 all: _firejail
 
 ROOT = ../..
-include $(ROOT)/src/common.mk
+include $(ROOT)/config.mk
 
 _firejail: _firejail.in
  gawk -f ../man/preproc.awk -- $(MANFLAGS) < $< > $@.tmp