Remove "Default search engine for Standard Mode"

🐞 Bug Report

Work needed from #44919 (closed)

(16.0 New/alpha vs 15.0 old/stable)

Reproduction steps

Settings -> Search -> Default search engine

Expected behaviour

"Normal browsing mode" settings should not show since we don't use it

User impact

Somewhat high as it is unused and could be misleading

Bookkeeping

• Browser version:
• Browser channel:
  • Release
  • Alpha
  • Nightly
• Distribution method:
  • Installer/archive from torproject.org
  • tor-browser-launcher
  • homebrew
  • other (please specify):
• Operating System:
  • Windows
    • Version:
  • macOS
    • Version:
  • Linux
    • Distribution + Version:
    • Desktop Environment + Version:
  • Android
    • Version:
    • Device:
  • Tails
  • Other (please specify):

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