Remove duplicate package Icon (#5818)

We were double-including the package icon after we started including
@(None) items in the package.

Remove the redundant item and use the same property as CSProj pack
target for specifying the Icon.

Author: ericstj

src/Microsoft.DotNet.Build.Tasks.Packaging/src/GenerateNuSpec.cs

@@ -205,7 +205,7 @@ private Manifest CreateManifest()
             }
             if (!string.IsNullOrEmpty(Icon))
             {
-                manifestMetadata.Icon = Path.GetFileName(Icon);
+                manifestMetadata.Icon = Icon;
             }
             manifestMetadata.UpdateMember(x => x.Id, Id);
             manifestMetadata.UpdateMember(x => x.Language, Language);
@@ -260,12 +260,7 @@ from f in Files.NullAsEmpty()
                     Target = f.GetMetadata(Metadata.FileTarget).Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar),
                     Exclude = f.GetMetadata(Metadata.FileExclude)
                 };
-            
-            if (!string.IsNullOrEmpty(Icon))
-            {
-                manifestFiles = manifestFiles.Append(new ManifestFile { Source = Icon, Target = Path.GetFileName(Icon) });
-            }
-            
+
             return manifestFiles.OrderBy(f => f.Target, StringComparer.OrdinalIgnoreCase).ToList();
         }
 

src/Microsoft.DotNet.Build.Tasks.Packaging/src/Microsoft.DotNet.Build.Tasks.Packaging.csproj

@@ -53,7 +53,6 @@
          so we must provide one.
          nuget's pack task treats _._ as special, to pack it must be in a folder on its own -->
     <None Include="build\content\_._" Pack="true" PackagePath="build\content\_._" />
-    <None Include="build\Icon.png" Pack="true" PackagePath="build\Icon.png" />
   </ItemGroup>
 
   <ItemGroup>

src/Microsoft.DotNet.Build.Tasks.Packaging/src/build/Icon.png

@@ -71,7 +71,6 @@
     <RuntimeFilePath Condition="'$(RuntimeFilePath)' == ''">$(NuSpecOutputPath)$(Id)$(NuspecSuffix)/runtime.json</RuntimeFilePath>
     <PackedPackageRuntimeFilePath Condition="'$(PackedPackageRuntimeFilePath)' == ''">$(NuSpecOutputPath)$(Id)$(NuspecSuffix)/$(PackedPackageNamePrefix).runtime.json</PackedPackageRuntimeFilePath>
     <PlaceholderFile>$(MSBuildThisFileDirectory)content/_._</PlaceholderFile>
-    <PackageIconFile Condition="'$(PackageIconFile)' == ''">$(MSBuildThisFileDirectory)Icon.png</PackageIconFile>
     <PackageDescriptionFile Condition="'$(PackageDescriptionFile)' == ''">path to descriptions.json must be specified</PackageDescriptionFile>
     <ValidationSuppressionFile Condition="'$(ValidationSuppressionFile)' == ''">ValidationSuppression.txt</ValidationSuppressionFile>
     <SyncInfoFile Condition="'$(SyncInfoFile)' == ''">unspecified</SyncInfoFile>
@@ -1211,7 +1210,7 @@
                     Language="$(Language)"
                     ProjectUrl="$(ProjectUrl)"
                     IconUrl="$(IconUrl)"
-                    Icon="$(PackageIconFile)"
+                    Icon="$(PackageIcon)"
                     LicenseUrl="$(LicenseUrl)"
                     PackageLicenseExpression="$(PackageLicenseExpression)"
                     Copyright="$(Copyright)"