UI: Tooltips: dont add period to labels

These are generally only one or two word phrases and are not sentences.
This change slightly improves readability.

Note, the check when display labels:

```
Tip Label (only for buttons not already showing the label).
```

Could be improved here because there are a lot of false positives.

source/blender/editors/interface/interface_region_tooltip.c

@@ -800,7 +800,7 @@ static uiTooltipData *ui_tooltip_data_from_button(bContext *C, uiBut *but)
                                                .style = UI_TIP_STYLE_HEADER,
                                                .color_id = UI_TIP_LC_NORMAL,
                                            });
-    field->text = BLI_sprintfN("%s.", but_label.strinfo);
+    field->text = BLI_sprintfN("%s", but_label.strinfo);
   }
 
   /* Tip */