Packaging: remove unsupported license expressions

We are still going to state Knuth-CTAN in the documentation, but there's
no way to tell this in NuGet metadata, unfortunately.

Author: ForNeVeR

src/AvaloniaMath/AvaloniaMath.csproj

@@ -8,7 +8,7 @@
     <PropertyGroup>
         <PackageId>AvaloniaMath</PackageId>
         <Title>Avalonia-Math</Title>
-        <PackageLicenseExpression>MIT AND Knuth-CTAN AND OFL-1.1</PackageLicenseExpression>
+        <PackageLicenseExpression>MIT AND OFL-1.1</PackageLicenseExpression>
         <PackageTags>$(PackageTags);avalonia</PackageTags>
         <Description>.NET library for rendering mathematical formulae using the LaTeX typsetting style, for the Avalonia framework.</Description>
     </PropertyGroup>

src/WpfMath/WpfMath.csproj

@@ -8,7 +8,7 @@
     <PropertyGroup>
         <PackageId>WpfMath</PackageId>
         <Title>WPF-Math</Title>
-        <PackageLicenseExpression>MIT AND Knuth-CTAN AND OFL-1.1</PackageLicenseExpression>
+        <PackageLicenseExpression>MIT AND OFL-1.1</PackageLicenseExpression>
         <Description>.NET library for rendering mathematical formulae using the LaTeX typsetting style, for the WPF framework.</Description>
         <PackageTags>$(PackageTags);wpf</PackageTags>
     </PropertyGroup>