uapi: move forward declarations of internal structures

Don't user forward declarations of internal kernel structures in headers
exported to userspace.

Move "struct completion;".
Move "struct task_struct;".

Link: http://lkml.kernel.org/r/20160713215808.GA22486@p183.telecom.bySigned-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/capability.h

@@ -38,6 +38,7 @@ struct cpu_vfs_cap_data {
 struct file;
 struct inode;
 struct dentry;
+struct task_struct;
 struct user_namespace;
 
 extern const kernel_cap_t __cap_empty_set;

include/linux/sysctl.h

@@ -28,6 +28,7 @@
 #include <uapi/linux/sysctl.h>
 
 /* For the /proc/sys support */
+struct completion;
 struct ctl_table;
 struct nsproxy;
 struct ctl_table_root;

include/uapi/linux/capability.h

@@ -15,8 +15,6 @@
 
 #include <linux/types.h>
 
-struct task_struct;
-
 /* User-level do most of the mapping between kernel and user
    capabilities based on the version tag given by the kernel. The
    kernel might be somewhat backwards compatible, but don't bet on

include/uapi/linux/sysctl.h

@@ -26,8 +26,6 @@
 #include <linux/types.h>
 #include <linux/compiler.h>
 
-struct completion;
-
 #define CTL_MAXNAME 10		/* how many path components do we allow in a
 				   call to sysctl?   In other words, what is
 				   the largest acceptable value for the nlen