fix double-application of highlight to definition node

Author: Tom Collings

lua/nvim-treesitter-refactor/highlight_definitions.lua

@@ -30,7 +30,7 @@ function M.highlight_usages(bufnr)
   local usages = locals.find_usages(def_node, scope, bufnr)
 
   for _, usage_node in ipairs(usages) do
-    if usage_node ~= node_at_point then
+    if usage_node ~= node_at_point and usage_node ~= def_node then
       ts_utils.highlight_node(usage_node, bufnr, usage_namespace, "TSDefinitionUsage")
     end
   end