Update .NET Core branding to .NET

Per the branding that .NET 5.0 is the next release after .NET Core 3.1.

ci/properties/dotnet-core.properties.json

@@ -1,6 +0,0 @@
-{
-    "name": ".NET Core",
-    "description": "Build and test a .NET Core or ASP.NET Core project.",
-    "iconName": "dotnetcore",
-    "categories": ["C#", "F#", "Visual Basic", "ASP", "ASP.NET", ".NET"]
-}

ci/properties/dotnet-desktop.properties.json

@@ -1,6 +1,6 @@
 {
-    "name": ".NET Core Desktop",
-    "description": "Build, test, sign and publish a desktop application built on .NET Core.",
-    "iconName": "dotnetcore",
+    "name": ".NET Desktop",
+    "description": "Build, test, sign and publish a desktop application built on .NET.",
+    "iconName": "dotnet",
     "categories": ["C#", "Visual Basic", "WPF", ".NET"]
 }

ci/properties/dotnet.properties.json

@@ -0,0 +1,6 @@
+{
+    "name": ".NET",
+    "description": "Build and test a .NET or ASP.NET Core project.",
+    "iconName": "dotnet",
+    "categories": ["C#", "F#", "Visual Basic", "ASP", "ASP.NET", ".NET"]
+}