Fix return value doc for Math.Asinh/MathF.Asinh (dotnet#7207)

Author: dstftw

xml/System/Math.xml

@@ -837,7 +837,7 @@
       <Docs>
         <param name="d">A number representing a hyperbolic sine, where <paramref name="d" /> must be greater than or equal to <see cref="F:System.Double.NegativeInfinity" />, but less than or equal to <see cref="F:System.Double.PositiveInfinity" />.</param>
         <summary>Returns the angle whose hyperbolic sine is the specified number.</summary>
-        <returns>An angle, θ, measured in radians, such that -∞ &lt; θ ≤ -1, or 1 ≤ θ &lt; ∞. 
+        <returns>An angle, θ, measured in radians. 
 
  -or-  
 

xml/System/MathF.xml

@@ -265,7 +265,7 @@ The static fields and methods of the `MathF` class correspond to those of the <x
       <Docs>
         <param name="x">A number representing a hyperbolic sine, where <paramref name="x" /> must be greater than or equal to <see cref="F:System.Single.NegativeInfinity" />, but less than or equal to <see cref="F:System.Single.PositiveInfinity" />.</param>
         <summary>Returns the angle whose hyperbolic sine is the specified number.</summary>
-        <returns>An angle, θ, measured in radians, such that -∞ &lt; θ ≤ -1, or 1 ≤ θ &lt; ∞. 
+        <returns>An angle, θ, measured in radians. 
 
  -or-