Updates example for as plain text rule (#235)

Co-authored-by: Mike F. Robbins <[email protected]>

Author: mikefrobbins

reference/docs-conceptual/PSScriptAnalyzer/Rules/AvoidUsingConvertToSecureStringWithPlainText.md

@@ -38,6 +38,4 @@ $EncryptedInput = ConvertTo-SecureString -String $UserInput -AsPlainText -Force
 
 ```powershell
 $SecureUserInput = Read-Host 'Please enter your secure code' -AsSecureString
-$EncryptedInput = ConvertFrom-SecureString -String $SecureUserInput
-$SecureString = ConvertTo-SecureString -String $EncryptedInput
 ```