Vastly improve Merge Doubles

- removed advanced merge doubles, it just does advanced by default
- same behavior as advanced was before, but now completes the task in under a second. Thanks to the power of BMesh!
- Labels now reflect this change

resources/translations/en_US.json

@@ -128,9 +128,7 @@
     "Optimization.combine_materials": "Combine Materials",
     "Optimization.combine_materials_desc": "Combine similar materials to reduce draw calls",
     "Optimization.remove_doubles": "Remove Doubles",
-    "Optimization.remove_doubles_desc": "Remove duplicate vertices",
-    "Optimization.remove_doubles_advanced": "Advanced",
-    "Optimization.remove_doubles_advanced_desc": "Remove duplicate vertices with advanced options",
+    "Optimization.remove_doubles_desc": "Remove duplicate vertices safely, keeping shapekeys preserved.",
     "Optimization.join_all_meshes": "Join All",
     "Optimization.join_all_meshes_desc": "Join all meshes in the scene",
     "Optimization.join_selected_meshes": "Join Selected",
@@ -158,8 +156,6 @@
     "Optimization.error.join_selected": "Failed to join selected meshes: {error}",
     "Optimization.merge_distance": "Merge Distance",
     "Optimization.merge_distance_desc": "Distance within which vertices will be merged",
-    "Optimization.remove_doubles_warning": "This process may take a long time",
-    "Optimization.remove_doubles_wait": "Blender may seem unresponsive during this operation",
     "Optimization.error.remove_doubles": "Failed to remove doubles: {error}",
     "Optimization.no_armature": "No armature selected",
     "Optimization.processing_mesh": "Processing mesh: {name}",