cgroup: make cgroup_is_removed() static

cgroup_is_removed() no longer has external users and it shouldn't grow
any - controllers should deal with cgroup_subsys_state on/offline
state instead of cgroup removal state.  Make it static.

While at it, make it return bool.
Signed-off-by: NTejun Heo <tj@kernel.org>

include/linux/cgroup.h

@@ -538,7 +538,6 @@ static inline const char *cgroup_name(const struct cgroup *cgrp)
 int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 
-int cgroup_is_removed(const struct cgroup *cgrp);
 bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);
 
 int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);

kernel/cgroup.c

@@ -226,7 +226,7 @@ static int css_refcnt(struct cgroup_subsys_state *css)
 }
 
 /* convenient tests for these bits */
-inline int cgroup_is_removed(const struct cgroup *cgrp)
+static inline bool cgroup_is_removed(const struct cgroup *cgrp)
 {
 	return test_bit(CGRP_REMOVED, &cgrp->flags);
 }