Remove obsolete MSVC check from pragma guard

 git grep -h -B1 "^#\s*pragma once" | grep -v pragma | sort | uniq

is now clean.
Functional: Remove obsolete MSVC version checks.
Functional: Remove obsolete GCC version checks.
Simplify SFINAE for largest float overload. Refs #8822.

I accidentally missed it out. Also fix the return values.
Change log.