Docs: Remove beta statement for External Control URCapX

[urfeex]

I think, it is safe to remove the beta notice from the PolyScope X External Control URCapX. We have released that in version 1.0.0 already and we have no outstanding work regarding feature parity with that URCapX.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.73%. Comparing base (1d785d9) to head (e42b444).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #407      +/-   ##
==========================================
- Coverage   42.82%   42.73%   -0.09%     
==========================================
  Files          99       99              
  Lines        8636     8632       -4     
  Branches     1171     1171              
==========================================
- Hits         3698     3689       -9     
- Misses       4659     4662       +3     
- Partials      279      281       +2     

Flag	Coverage Δ
start_ursim	81.78% <ø> (-2.89%)	⬇️
ur20-latest	40.72% <ø> (-0.05%)	⬇️
ur5-3.14.3	40.56% <ø> (ø)
ur5e-10.7.0	35.64% <ø> (-0.05%)	⬇️
ur5e-5.9.4	40.66% <ø> (+<0.01%)	⬆️

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