Doc/Michelson: redirect control structures to interactive reference.

Context

Answers this part of #4077:

• delete the parts about instructions from the static reference:
  • Control structures

The documentation about all the control structure instructions in the interactive reference contains that found in the static reference.
It was checked manually by comparing the static and interactive documentations for each control structure instruction of the static reference.

Manually testing the MR

make -C docs -j

And then open docs/_build/alpha/michelson.html#control-structures in a web browser.

Checklist

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