doc: Remove wibox prefixes

This produced the wrong output in awful.wibar documentation

docs/common/wibox.ldoc

@@ -164,20 +164,20 @@
 --- Get or set mouse buttons bindings to a wibox.
 --
 -- @param buttons_table A table of buttons objects, or nothing.
--- @function wibox.buttons
+-- @function buttons
 
 --- Get or set wibox geometry. That's the same as accessing or setting the x,
 -- y, width or height properties of a wibox.
 --
 -- @param A table with coordinates to modify.
 -- @return A table with wibox coordinates and geometry.
--- @function wibox.geometry
+-- @function geometry
 
 --- Get or set wibox struts.
 --
 -- @param strut A table with new strut, or nothing
 -- @return The wibox strut in a table.
--- @function wibox.struts
+-- @function struts
 -- @see client.struts
 
 --- The default background color.