Clean up comments for LWG-3912 `enumerate_view::iterator::operator-` should be `noexcept`

[frederick-vs-ja]

LWG-3912 has been voted into the standard, so we should remove the following /* strengthened */ comment.

Code:

STL/stl/inc/ranges

Lines 6126 to 6129 in 15aea98

	_NODISCARD_FRIEND constexpr difference_type operator-(
	const _Iterator& _Left, const _Iterator& _Right) noexcept /* strengthened */ {
	return _Left._Pos - _Right._Pos;
	}

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