message: docs(changelog): remove empty sections
  The changelog contains some empty sections (such as `### Bug Fixes`). This change removes these empty sections.
  PR Close
diff: @@ -2431,14 +2431,6 @@ This release contains various API docs improvements.
  # [8.0.0-beta.0](https://github.com/angular/angular/compare/7.2.0...8.0.0-beta.0) (2019-01-16)
  -### Bug Fixes
  -
  -
  -
  -### Features
  -
  -
  -
  ### Performance Improvements
  @@ -2586,10 +2578,6 @@ This release contains various API docs improvements.
  # [7.1.0](https://github.com/angular/angular/compare/7.1.0-rc.0...7.1.0) (2018-11-21)
  -### Bug Fixes
  -
  -
  -
  ### Features
  * **bazel:** Bazel workspace schematics ([#26971](https://github.com/angular/angular/issues/26971)) ([b07bd30](https://github.com/angular/angular/commit/b07bd30))
  @@ -3726,9 +3714,6 @@ Note: Due to an animation fix back in 5.1.1 ([c2b3792](https://github.com/angula
  <a name="5.1.0-beta.0"></a>
  # [5.1.0-beta.0](https://github.com/angular/angular/compare/5.0.0-rc.4...5.1.0-beta.0) (2017-11-08)
  -### Bug Fixes
  -
  -
  ### Features
  * **compiler:** introduce `TestBed.overrideTemplateUsingTestingModule` ([a460066](https://github.com/angular/angular/commit/a460066)), closes [#19815](https://github.com/angular/angular/issues/19815)
  