Remove 2018 deprecated runtime contenttype extension point

[vogella]

In 2018 we marked this extension point for deletion, lets remove it for 2025-03.

[github-actions[bot]]

Test Results

 1 674 files  +  504   1 674 suites  +504   1h 45m 52s ⏱️ + 49m 39s  4 017 tests  -   153   3 989 ✅  -   135   22 💤  - 24   6 ❌ + 6  12 648 runs  +3 910  12 466 ✅ +3 845  164 💤 +47  18 ❌ +18 

For more details on these failures, see this check.

Results for commit 3a2947f1. ± Comparison against base commit d974aaf9.

This pull request removes 153 tests.

``` AllCompareTests AsyncExecTests ‑ testCancelOnRequeue AllCompareTests AsyncExecTests ‑ testQueueAdd AllCompareTests AsyncExecTests ‑ testWorker AllCompareTests CompareFileRevisionEditorInputTest ‑ testPrepareCompareInputWithNonLocalResourceTypedElements AllCompareTests CompareUIPluginTest ‑ testFindContentViewerDescriptorForTextType_StreamAccessor AllCompareTests CompareUIPluginTest ‑ testFindContentViewerDescriptor_TextType_NotStreamAccessor AllCompareTests CompareUIPluginTest ‑ testFindContentViewerDescriptor_UnknownType AllCompareTests ContentMergeViewerTest ‑ testFFFX AllCompareTests ContentMergeViewerTest ‑ testFFTX AllCompareTests ContentMergeViewerTest ‑ testFFXF … ```