Remove file change detection

Turns out that there's no reliable way of figuring out whether a plaintext
file is no longer being edited in a text editor, so don't bother with it.
Instead, display a messagebox asking the user whether they want to encrypt
or discard their changes as soon as the file is opened, allowing them to
click yes or no when they're finished.

It's not exactly pretty, but it's better than running the risk of leaving
plaintext files in the password store without the user knowing.

pass-winmenu/src/Program.cs

@@ -502,46 +502,7 @@ private void EditPassword()
 			// Open the file in the user's default editor
 			var proc = Process.Start(plaintextFile);
 
-			// Wait for the text file to be written to
-			while (File.GetLastWriteTime(plaintextFile) < startTime)
-			{
-				Thread.Sleep(1000);
-				if ((DateTime.Now - startTime).Hours >= 2)
-				{
-					try
-					{
-						File.Delete(plaintextFile);
-					}
-					catch (IOException) { }
-					return;
-				}
-			}
-			// Wait for the file to be closed
-			bool inUse = true;
-			while (inUse)
-			{
-				try
-				{
-					var stream = File.Open(plaintextFile, FileMode.Open, FileAccess.Read, FileShare.None);
-					inUse = false;
-					stream.Close();
-				}
-				catch (IOException)
-				{
-					Thread.Sleep(1000);
-				}
-				if ((DateTime.Now - startTime).Hours >= 2)
-				{
-					try
-					{
-						File.Delete(plaintextFile);
-					}
-					catch (IOException) { }
-					return;
-				}
-			}
-
-			var result = MessageBox.Show($"Do you want to encrypt and save your changes to {Path.GetFileName(selectedFile)}?", "Edit password file", MessageBoxButton.YesNo, MessageBoxImage.Question);
+			var result = MessageBox.Show("Please keep this window open until you're done editing the password file.\nThen click Yes to save your changes, or No to discard them.", $"Save changes to {Path.GetFileName(selectedFile)}?", MessageBoxButton.YesNo, MessageBoxImage.Information);
 
 			if (result != MessageBoxResult.Yes)
 			{