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: Tejun Heo <tj@kernel.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a19419f..5019748 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -226,7 +226,7 @@
 }
 
 /* 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);
 }