CLEANUP: contrib: remove the last references to the now dead contrib/ directory

Now with the last SPOA modules gone, contrib/ doesn't exist anymore
and does not need to be referenced in the Makefile nor .gitignore.

.gitignore

@@ -19,7 +19,6 @@
 !/SUBVERS
 !/VERDATE
 !/VERSION
-!/contrib
 !/admin
 !/dev
 !/doc

CONTRIBUTING

@@ -818,9 +818,7 @@ exhaustive:
 
   - poll      any of the pollers
 
-  - halog     the halog sub-component in the contrib directory
+  - halog     the halog sub-component in the admin directory
-
-  - contrib   any addition to the contrib directory
 
   - htx       general HTX subsystem
 

Makefile

@@ -1008,7 +1008,7 @@ clean:
 	$(Q)for dir in . src dev/* admin/* addons/* include/* doc; do rm -f $$dir/*~ $$dir/*.rej $$dir/core; done
 	$(Q)rm -f haproxy-$(VERSION).tar.gz haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
 	$(Q)rm -f haproxy-$(VERSION) haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION) nohup.out gmon.out
-	$(Q)rm -f {admin,dev,contrib}/*/*.[oas] {admin,dev,contrib}/*/*/*.[oas] {admin,dev,contrib}/*/*/*/*.[oas]
+	$(Q)rm -f {admin,dev}/*/*.[oas] {admin,dev}/*/*/*.[oas] {admin,dev}/*/*/*/*.[oas]
 	$(Q)rm -f addons/promex/*.[oas]
 	$(Q)rm -f addons/51degrees/*.[oas] addons/51degrees/dummy/*.[oas] addons/51degrees/dummy/*/*.[oas]
 	$(Q)rm -f addons/deviceatlas/*.[oas] addons/deviceatlas/dummy/*.[oas]