Remove experimental threads disclaimer

[germain-gg]

Threads are now in a public beta, this disclaimer is not needed anymore

Closes element-hq/element-web#22088.

---

This change is marked as an internal change (Task), so will not be included in the changelog.

[t3chguy]

[codecov]

Codecov Report

Merging #8445 (b71c780) into develop (3e31fdb) will decrease coverage by 0.06%.
The diff coverage is n/a.

❗ Current head b71c780 differs from pull request most recent head 40c0aa8. Consider uploading reports for the commit 40c0aa8 to get more accurate results

@@             Coverage Diff             @@
##           develop    #8445      +/-   ##
===========================================
- Coverage    30.85%   30.78%   -0.07%     
===========================================
  Files          893      893              
  Lines        50793    50767      -26     
  Branches     12928    12920       -8     
===========================================
- Hits         15671    15628      -43     
- Misses       35122    35139      +17     

Impacted Files	Coverage Δ
src/components/structures/MatrixChat.tsx	0.00% <ø> (ø)
src/components/views/rooms/SearchBar.tsx	0.00% <0.00%> (-89.29%)	⬇️
src/components/views/rooms/ReadReceiptGroup.tsx	8.33% <0.00%> (-21.67%)	⬇️
src/events/EventTileFactory.tsx	66.66% <0.00%> (-0.36%)	⬇️
src/components/views/rooms/EventTile.tsx	46.34% <0.00%> (-0.11%)	⬇️
src/contexts/RoomContext.ts	100.00% <0.00%> (ø)
src/components/structures/RoomView.tsx	29.65% <0.00%> (ø)
src/components/views/right_panel/UserInfo.tsx	29.23% <0.00%> (ø)
src/Lifecycle.ts	1.42% <0.00%> (+<0.01%)	⬆️
...gs/handlers/AbstractLocalStorageSettingsHandler.ts	76.31% <0.00%> (+1.31%)	⬆️