Remove stale entries from Unreleased section.
# Unreleased
-* [fixed] Fixed a bug where screen traces were not capturing frame metrics for multi-activity apps.
-* [feature] Added support for measuring screen performance metrics for "Activity Fragments" out-of-the-box.
-* [fixed] Excluded custom attributes whose key/value length is 0.
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# 20.2.0
* [unchanged] Updated to accommodate the release of the updated
[perfmon] Kotlin extensions library.
