Stats: Remove redundant docs, remove unused method

This patch does some cosmetic changes to the Stats library like:
- Remove some redundant class properties doc especially when file
  is in strict type mode
- Cleanup class level doc that adds little meaning to what the class
  already does
- Remove unused `mergeLabels()` method. This can be directly removed
  without deprecation, as the feature ended up never being used in
  the first place and it's only here because during the efforts in
  I60c497727fdae493c3bb18de3bd1a4db338132cc, we forgot to remove this
  particular method.

This patch also fixes a phan issue that detected that `getMetric()`
in StatsFactory class calls BaseMetric::withStatsdDataFactory() with
a null because the member's default value is null but doesn't say
this in the BaseMetricInterface, this fixes it.

Change-Id: Id9fbdeed3e8cd9ddd9e48031139b4f31c40c2558

1 files changed, 3 insertions, 2 deletions

diff --git a/includes/libs/Stats/Metrics/BaseMetricInterface.php b/includes/libs/Stats/Metrics/BaseMetricInterface.php
index f3113619e76a..611f54d1c1e6 100644
--- a/includes/libs/Stats/Metrics/BaseMetricInterface.php
+++ b/includes/libs/Stats/Metrics/BaseMetricInterface.php
@@ -156,8 +156,9 @@ interface BaseMetricInterface {
 	/**
 	 * StatsD Data Factory instance to copy metrics to.
 	 *
-	 * @param IBufferingStatsdDataFactory $statsdDataFactory
+	 * @param IBufferingStatsdDataFactory|null $statsdDataFactory
+	 *
 	 * @return BaseMetricInterface
 	 */
-	public function withStatsdDataFactory( IBufferingStatsdDataFactory $statsdDataFactory );
+	public function withStatsdDataFactory( ?IBufferingStatsdDataFactory $statsdDataFactory );
 }