remove method conj from Numeric per issue 3782

[arkiuat]

The problem

method .conj is currently documented in Complex, Cool, and Numeric, but the last entry doesn't correspond to anything tested in roast, while the first two can at least be interpreted as corresponding with the two places in roast where .conj is tested.

Solution provided

deleted the entry for this method in doc/Type/Numeric.rakudoc (sorry for the typo in the commit msg)

[arkiuat]

Marking this as draft until the discussion in issue 3782 concludes.

Might also want to change the example code in Cool's entry for method conj to show it used against a Str, since the example currently there would do just as well in Complex as in Cool, and Complex.conj already has its own doc.