doc: Cleanup how methods are rendered in the doc.

Previously, there was some `module:foo()` or `gears.object:foo()`
because the doc used the "raw" name and/or, in some undefined and
race condition prone (due to `pairs()` order), the formatted
"classmod" name.

Now, just display `:foo()` and be done with it.

docs/config.ld

@@ -163,7 +163,13 @@ custom_display_name_handler = function(item, default_handler)
         return default_handler(item) .. "</a> <i class=\"deprecated_label\">[deprecated]</i><a>"
     end
 
-    return default_handler(item)
+    local ret = default_handler(item)
+
+    -- Get rid of the "module:" in front of method names. It is either wrong or
+    -- just redundant.
+    ret = ret:gsub("([^:]*)(:[^:])","%2")
+
+    return ret
 end
 
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