Clean-up platform-specific conditions

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs

@@ -60,7 +60,7 @@ public static Process Start(string fileName, string arguments, string userName,
         [UnsupportedOSPlatform("tvos")]
         public void Kill()
         {
-            if ((OperatingSystem.IsIOS() && !OperatingSystem.IsMacCatalyst()) || OperatingSystem.IsTvOS())
+            if (!PlatformSupportsProcessStartAndKill)
             {
                 throw new PlatformNotSupportedException();
             }
@@ -372,7 +372,7 @@ private SafeProcessHandle GetProcessHandle()
         /// <param name="startInfo">The start info with which to start the process.</param>
         private bool StartCore(ProcessStartInfo startInfo)
         {
-            if ((OperatingSystem.IsIOS() && !OperatingSystem.IsMacCatalyst()) || OperatingSystem.IsTvOS())
+            if (!PlatformSupportsProcessStartAndKill)
             {
                 throw new PlatformNotSupportedException();
             }
@@ -1105,5 +1105,8 @@ private static int OnSigChild(int reapAll, int configureConsole)
                 s_processStartLock.ExitWriteLock();
             }
         }
+
+        private static bool PlatformSupportsProcessStartAndKill
+            => (!OperatingSystem.IsIOS() || OperatingSystem.IsMacCatalyst()) && !OperatingSystem.IsTvOS();
     }
 }