remove some redundant constructor overloads from exceptions (#979)

* remove some redundant constructor overloads from exceptions

* re add ImageProcessingException ctor

only used in release

src/ImageSharp/Common/Exceptions/UnknownImageFormatException.cs

@@ -1,8 +1,6 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using System;
-
 namespace SixLabors.ImageSharp
 {
     /// <summary>
@@ -20,17 +18,5 @@ namespace SixLabors.ImageSharp
             : base(errorMessage)
         {
         }
-
-        /// <summary>
-        /// Initializes a new instance of the <see cref="UnknownImageFormatException"/> class with a specified
-        /// error message and the exception that is the cause of this exception.
-        /// </summary>
-        /// <param name="errorMessage">The error message that explains the reason for this exception.</param>
-        /// <param name="innerException">The exception that is the cause of the current exception, or a null reference (Nothing in Visual Basic)
-        /// if no inner exception is specified.</param>
-        public UnknownImageFormatException(string errorMessage, Exception innerException)
-            : base(errorMessage, innerException)
-        {
-        }
     }
 }