vfs: Remove duplicated d_mountpoint check in __is_local_mountpoint

vfs: Remove duplicated d_mountpoint check in __is_local_mountpoint

This function acts as an out-of-line helper for is_local_mountpoint
is only called after the latter verifies the dentry is not a mountpoint.
There's no semantic changes and the resulting object code is smaller:

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-26 (-26)
Function                                     old     new   delta
__is_local_mountpoint                        147     121     -26
Total: Before=34161, After=34135, chg -0.08%

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>