System.Memory should be referenced conditionally

Author: michaelklishin

projects/RabbitMQ.Client/RabbitMQ.Client.csproj

@@ -56,7 +56,6 @@
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
 
     <PackageReference Include="MinVer" Version="2.4.0" PrivateAssets="All" />
-    <PackageReference Include="System.Memory" Version="4.5.4" />
     <PackageReference Include="System.Threading.Channels" Version="4.7.1" />
   </ItemGroup>