PipelineRun timeouts is in Beta

`PipelineRun` timeouts were promoted to Beta. This change removes
the listing of `PipelineRun` timeouts from the alpha features.

Issue: #4460
PR: #4813

docs/install.md

@@ -419,7 +419,6 @@ Features currently in "alpha" are:
 | [`Runs` and `Custom Tasks`](./runs.md)                                                                | [TEP-0002](https://github.com/tektoncd/community/blob/main/teps/0002-custom-tasks.md)                                | [v0.19.0](https://github.com/tektoncd/pipeline/releases/tag/v0.19.0) | `enable-custom-tasks`       |
 | [Isolated `Step` & `Sidecar` `Workspaces`](./workspaces.md#isolated-workspaces)                       | [TEP-0029](https://github.com/tektoncd/community/blob/main/teps/0029-step-workspaces.md)                             | [v0.24.0](https://github.com/tektoncd/pipeline/releases/tag/v0.24.0) |                             |
 | [Hermetic Execution Mode](./hermetic.md)                                                              | [TEP-0025](https://github.com/tektoncd/community/blob/main/teps/0025-hermekton.md)                                   | [v0.25.0](https://github.com/tektoncd/pipeline/releases/tag/v0.25.0) |                             |
-| [`PipelineRun` Timeouts](./pipelineruns.md#configuring-a-failure-timeout)                             | [TEP-0046](https://github.com/tektoncd/community/blob/main/teps/0046-finallytask-execution-post-timeout.md)          | [v0.25.0](https://github.com/tektoncd/pipeline/releases/tag/v0.25.0) |                             |
 | [Implicit `Parameters`](./taskruns.md#implicit-parameters)                                            | [TEP-0023](https://github.com/tektoncd/community/blob/main/teps/0023-implicit-mapping.md)                            | [v0.28.0](https://github.com/tektoncd/pipeline/releases/tag/v0.28.0) |                             |
 | [Windows Scripts](./tasks.md#windows-scripts)                                                         | [TEP-0057](https://github.com/tektoncd/community/blob/main/teps/0057-windows-support.md)                             | [v0.28.0](https://github.com/tektoncd/pipeline/releases/tag/v0.28.0) |                             |
 | [Remote Tasks](./taskruns.md#remote-tasks) and [Remote Pipelines](./pipelineruns.md#remote-pipelines) | [TEP-0060](https://github.com/tektoncd/community/blob/main/teps/0060-remote-resolutiond.md)                          |                                                                      |                             |