Drop unused tags from histograms print_style

tools/metrics/histograms/print_style.py

Index: tools/metrics/histograms/print_style.py
diff --git a/tools/metrics/histograms/print_style.py b/tools/metrics/histograms/print_style.py
index ebd65b95d206f4be399c3a4e2c094a498856c4da..6b7064990c6141bb812ef69f4b3361a0c8ac26ca 100644
--- a/tools/metrics/histograms/print_style.py
+++ b/tools/metrics/histograms/print_style.py
@@ -16,24 +16,19 @@ import pretty_print_xml
 # { tag_name: [attribute_name, ...] }
 ATTRIBUTE_ORDER = {
     'affected-histogram': ['name'],
-    'detail': [],
     'details': [],
     'enum': ['name', 'type'],
     'enums': [],
-    # TODO(yiyaoliu): Remove fieldtrial related pieces when it is not used.
-    'fieldtrial': ['name', 'separator', 'ordering'],
     'histogram': ['base', 'name', 'enum', 'units'],
     'histogram-configuration': ['logsource'],
     'histogram_suffixes': ['name', 'separator', 'ordering'],
     'histogram_suffixes_list': [],
     'histograms': [],
     'int': ['value', 'label'],
-    'group': ['name', 'label'],
     'obsolete': [],
     'owner': [],
     'suffix': ['base', 'name', 'label'],
     'summary': [],
-    'with-group': ['name'],
     'with-suffix': ['name'],
 }