Update stride package definitions to use a license expression of 'MIT' rather than the deprecated licenseUrl.

sources/launcher/Stride.Launcher/Stride.Launcher.nuspec

@@ -5,7 +5,7 @@
     <version>5.0.6</version>
     <authors>Stride</authors>
     <owners>Stride</owners>
-    <licenseUrl>https://stride3d.net/license.txt</licenseUrl>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <projectUrl>https://stride3d.net/</projectUrl>
     <copyright>&#169; Stride contributors and Silicon Studio Corp.</copyright>
     <description>Stride Launcher

sources/targets/Stride.PackageVersion.targets

@@ -15,7 +15,7 @@
     <StrideNuGetVersion>$(StridePublicVersion)$(StrideNuGetVersionSuffix)$(StrideBuildMetadata)</StrideNuGetVersion>
     
     <PackageVersion Condition=" '$(PackageVersion)' == '' ">$(StrideNuGetVersion)</PackageVersion>
-    <PackageLicenseUrl>https://github.com/stride3d/stride/blob/master/LICENSE.md</PackageLicenseUrl>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageProjectUrl>https://stride3d.net</PackageProjectUrl>
     <PackageIcon>nuget-icon.png</PackageIcon>
     <RepositoryUrl>https://github.com/stride3d/stride</RepositoryUrl>

sources/tools/Stride.VisualStudio.Package/Stride.VisualStudio.Package.nuspec

@@ -5,7 +5,7 @@
     <version>4.1.0</version>
     <authors>Stride</authors>
     <owners>Stride</owners>
-    <licenseUrl>https://github.com/stride3d/stride/blob/master/LICENSE.md</licenseUrl>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <projectUrl>http://stride3d.net/</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/stride3d/media/master/images/mainlogo/nuget/logo.png</iconUrl>
     <repository type="git" url="https://github.com/stride3d/stride" />