mount.2: Remove a couple of obsolete EBUSY errors

As far as I can tell, these EBUSY errors disappeared
with the addition of stackable mounts in Linux 2.4.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/mount.2

@@ -586,10 +586,6 @@ option.
 .\" the error EPERM if not present; CAP_DAC_OVERRIDE is required.
 .TP
 .B EBUSY
-.I source
-is already mounted.
-.TP
-.B EBUSY
 An attempt was made to stack a new mount directly on
 top of an existing mount point that was created in this
 mount namespace with the same
@@ -602,15 +598,6 @@ and
 cannot be remounted read-only,
 because it still holds files open for writing.
 .TP
-.B EBUSY
-.I source
-cannot be mounted on
-.I target
-because
-.I target
-is still busy (it is the working directory of some thread,
-the mount point of another device, has open files, etc.).
-.TP
 .B EFAULT
 One of the pointer arguments points outside the user address space.
 .TP