protocol: Hyphenate compound adjective surface-local

Remove superfluous 'local' from 'buffer local'.
In addition, simplify the phrasing of local x/y coordinates in parameter
summaries.

See https://lists.freedesktop.org/archives/wayland-devel/2016-April/028249.html

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Signed-off-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>