chore: remove PLAYWRIGHT_INPUT_FILE_TEXTBOX

[dgozman]

This was an escape hatch for a possibly breaking change. There are no usages on GitHub as of today, so seems safe to remove.

[github-actions]

Test results for "tests 1"

6 flaky

⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:986:7 › cli codegen › should not throw csp directive violation errors @firefox-ubuntu-22.04-node18
⚠️ [firefox-library] › library/inspector/cli-codegen-aria.spec.ts:76:7 › should update aria snapshot highlight @firefox-ubuntu-22.04-node18
⚠️ [firefox-page] › page/page-wait-for-function.spec.ts:104:3 › should work with strict CSP policy @firefox-ubuntu-22.04-node18
⚠️ [webkit-page] › page/page-event-popup.spec.ts:28:3 › should work with window features @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › page/page-set-input-files.spec.ts:38:5 › should upload a folder @webkit-ubuntu-22.04-node18
⚠️ [playwright-test] › ui-mode-test-watch.spec.ts:145:5 › should watch all @windows-latest-node18-1

39314 passed, 816 skipped
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Merge workflow run.