Remove obsolete fieldtrial related code.

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 ed8dc3a5792782a9b514a92186a022b818b8119a..e09f762ad8930ebc33e174f1a8a347459e2a8b8b 100644
--- a/tools/metrics/histograms/print_style.py
+++ b/tools/metrics/histograms/print_style.py
@@ -20,11 +20,7 @@ ATTRIBUTE_ORDER = {
   'int': ['value', 'label'],
   'histogram_suffixes': ['name', 'separator', 'ordering'],
   'suffix': ['name', 'label'],
-  # TODO(yiyaoliu): Remove fieldtrial related pieces when it is not used.
-  'fieldtrial': ['name', 'separator', 'ordering'],
-  'group': ['name', 'label'],
   'affected-histogram': ['name'],
-  'with-group': ['name'],
   'with-suffix': ['name'],
 }
 
@@ -33,8 +29,6 @@ TAGS_THAT_DONT_INDENT = [
   'histogram-configuration',
   'histograms',
   'histogram_suffixes_list',
-  # TODO(yiyaoliu): Remove fieldtrial related pieces when it is not used.
-  'fieldtrials',
   'enums'
 ]
 
@@ -43,14 +37,11 @@ TAGS_THAT_DONT_INDENT = [
 TAGS_THAT_HAVE_EXTRA_NEWLINE = {
   'histogram-configuration': (2, 1, 1),
   'histograms': (2, 1, 1),
-  # TODO(yiyaoliu): Remove fieldtrial related pieces when it is not used.
-  'fieldtrials': (2, 1, 1),
+  'histogram': (1, 1, 1),
   'histogram_suffixes_list': (2, 1, 1),
   'histogram_suffixes': (1, 1, 1),
   'enums': (2, 1, 1),
-  'histogram': (1, 1, 1),
   'enum': (1, 1, 1),
-  'fieldtrial': (1, 1, 1),
 }
 
 # Tags that we allow to be squished into a single line for brevity.