Gaussian distributions have no atoms

This is kept in a separate file to avoid importing probability theory elsewhere.

theorem MeasureTheory.NoAtoms'.gaussianReal {μ : ℝ} {v : NNReal} (h : v ≠ 0) : NoAtoms' (ProbabilityTheory.gaussianReal μ v)

Analogue of ProbabilityTheory.nullSingletonClass_gaussianReal for NoAtoms'.