Remove unimplemented Utility cmdlets from Unix

ConvertFrom-SddlString and Unblock-File are Windows-specific cmdlets
with no equivalent on Unix.

squash! Remove Unblock-File from Unix

src/Modules/Unix/Microsoft.PowerShell.Utility/Microsoft.PowerShell.Utility.psd1

@@ -21,10 +21,9 @@ CmdletsToExport= "Format-List", "Format-Custom", "Format-Table", "Format-Wide",
     "Write-Verbose", "Write-Warning", "Write-Error", "Write-Information", "Write-Output", "Set-PSBreakpoint",
     "Get-PSBreakpoint", "Remove-PSBreakpoint", "Enable-PSBreakpoint", "Disable-PSBreakpoint", "Get-PSCallStack",
     "Get-TraceSource", "Set-TraceSource", "Trace-Command",
-    "Unblock-File", "Get-Runspace", "Debug-Runspace", "Enable-RunspaceDebug", "Disable-RunspaceDebug",
+    "Get-Runspace", "Debug-Runspace", "Enable-RunspaceDebug", "Disable-RunspaceDebug",
     "Get-RunspaceDebug", "Wait-Debugger" 
-FunctionsToExport= "Get-FileHash", "New-TemporaryFile", "New-Guid", "Format-Hex", "Import-PowerShellDataFile",
-    "ConvertFrom-SddlString"
+FunctionsToExport= "Get-FileHash", "New-TemporaryFile", "New-Guid", "Format-Hex", "Import-PowerShellDataFile"
 AliasesToExport= "fhx"
 NestedModules="Microsoft.PowerShell.Commands.Utility.dll","Microsoft.PowerShell.Utility.psm1"
 HelpInfoURI = 'http://go.microsoft.com/fwlink/?linkid=390787'

test/powershell/Modules/Microsoft.PowerShell.Utility/Unimplemented-Cmdlet.Tests.ps1

@@ -0,0 +1,13 @@
+Describe "Unimplemented Utility Cmdlet Tests" -Tags "CI" {
+
+    $Commands = @(
+        "Unblock-File",
+        "ConvertFrom-SddlString"
+    )
+
+    foreach ($Command in $Commands) {
+        It "$Command should only be available on Windows" {
+            [bool](Get-Command $Command -ErrorAction SilentlyContinue) | Should Be $IsWindows
+        }
+    }
+}