reduce xunit refs

fixes #649

Author: SimonCropp

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;xUnit1026;xUnit1013;msb3277;CS0436</NoWarn>
-    <Version>18.0.0-beta.17</Version>
+    <Version>18.0.0-beta.18</Version>
     <ImplicitUsings>enable</ImplicitUsings>
     <LangVersion>preview</LangVersion>
     <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings>

src/Verify.Xunit/Verify.Xunit.csproj

@@ -9,9 +9,7 @@
     <Using Include="Xunit.Sdk" />
     <Using Include="VerifyTests" />
     <Using Include="Argon" />
-    <PackageReference Include="xunit.assert" Version="2.4.2" />
     <PackageReference Include="xunit.abstractions" Version="2.0.3" />
-    <PackageReference Include="xunit.extensibility.execution" Version="2.4.2" />
     <PackageReference Include="ProjectDefaults" Version="1.0.80" PrivateAssets="all" />
     <PackageReference Include="EmptyFiles" Version="2.8.0" PrivateAssets="None" />
     <PackageReference Include="IndexRange" Version="1.0.2" PrivateAssets="all" />