Revert "Add WebKit to e2e test matrix (#37298)" (#37315)

Reverts: #37298
Ref:
https://github.com/go-gitea/gitea/actions/runs/24661464168/job/72108324223?pr=37312

WebKit on Linux has a long history of flakiness in Playwright CI runs,
and the exact "WebKit encountered an internal error" class of failures
has been reported repeatedly and closed without a real fix (typically
stale/no-repro, or worked around by retries):

- https://github.com/microsoft/playwright/issues/34450
- https://github.com/microsoft/playwright/issues/35773
- https://github.com/microsoft/playwright/issues/35870
- https://github.com/microsoft/playwright/issues/35293
- https://github.com/microsoft/playwright/issues/38838

Keeping chromium and firefox in the e2e matrix.

---
This PR was written with the help of Claude Opus 4.7

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

playwright.config.ts

@@ -36,11 +36,5 @@ export default defineConfig({
         ...devices['Desktop Firefox'],
       },
     },
-    {
-      name: 'webkit',
-      use: {
-        ...devices['Desktop Safari'],
-      },
-    },
   ],
 });