Help: Drop incorrect versionadded for try_compile result variable

In !5481 (merged) we accidentally added versionadded markup suggesting that the first argument to try_compile was fixed as RESULT_VAR prior to CMake 3.14. This was probably due to misinterpreting the change from !3013 (merged).

The result variable has never been fixed. Drop the incorrect markup.

Original Description

The first argument has not been fixed for at least 15 years, well before 3.0 - or 3.14 for that matter - has been released.

Is this intentional? Was this just overlooked? Was it an "undocumented" feature?
If possible, this should also be backported to the old versions' reference documentation on the CMake website.

The git history says that it was practically never fixed to anything and the commit that added the note is a massive commit that just adds a bunch of these version notes, so it's extra confusing.
Came across this when writing my own Check module.

Backport: release