Simplify implementation of merge() for DataTree (#10844)

Author: shoyer

xarray/structure/merge.py

@@ -795,7 +795,7 @@ def merge_core(
 
 
 def merge_trees(
-    trees: Iterable[DataTree],
+    trees: Sequence[DataTree],
     compat: CompatOptions | CombineKwargDefault = _COMPAT_DEFAULT,
     join: JoinOptions | CombineKwargDefault = _JOIN_DEFAULT,
     fill_value: object = dtypes.NA,
@@ -839,18 +839,6 @@ def level(kv):
                 join=join,
                 combine_attrs=combine_attrs,
             )
-        # Remove inherited coordinates/indexes/dimensions.
-        for var_name in list(merge_result.coord_names):
-            if not any(var_name in node._coord_variables for node in nodes):
-                del merge_result.variables[var_name]
-                merge_result.coord_names.remove(var_name)
-        for index_name in list(merge_result.indexes):
-            if not any(index_name in node._node_indexes for node in nodes):
-                del merge_result.indexes[index_name]
-        for dim in list(merge_result.dims):
-            if not any(dim in node._node_dims for node in nodes):
-                del merge_result.dims[dim]
-
         merged_ds = Dataset._construct_direct(**merge_result._asdict())
         result[key] = DataTree(dataset=merged_ds)