Remove region diagnostics setting

Part of #292934

This is an implementation detail. Was only really added in 5.6 in case the new behavior caused issues. Should be safe to remove now

extensions/typescript-language-features/package.json

@@ -452,12 +452,6 @@
             "markdownDescription": "%typescript.workspaceSymbols.excludeLibrarySymbols%",
             "scope": "window"
           },
-          "typescript.tsserver.enableRegionDiagnostics": {
-            "type": "boolean",
-            "default": true,
-            "description": "%typescript.tsserver.enableRegionDiagnostics%",
-            "scope": "window"
-          },
           "javascript.updateImportsOnPaste.enabled": {
             "scope": "window",
             "type": "boolean",