[swcomp] Replace ConvertibleFromString extension for BZip2.BlockSize with an empty conformance

SwiftCLI provides a default implementation for enums with Int raw values.

Sources/swcomp/Archives/BZip2Command.swift

@@ -7,6 +7,11 @@ import Foundation
 import SWCompression
 import SwiftCLI
 
+// This extension allows to use BZip2.BlockSize as a Key option.
+// The extension is empty because there is a default implementation for a ConvertibleFromString when the RawValue type
+// of the enum (Int, in this case) is ConvertibleFromString itself.
+extension BZip2.BlockSize: ConvertibleFromString {}
+
 class BZip2Command: Command {
 
     let name = "bz2"

Sources/swcomp/Extensions/BlockSize+ConvertibleFromString.swift

@@ -1,19 +0,0 @@
-// Copyright (c) 2021 Timofey Solomko
-// Licensed under MIT License
-//
-// See LICENSE for license information
-
-import Foundation
-import SwiftCLI
-import SWCompression
-
-/// This extension allows to use `BlockSize` as a `Key` option.
-extension BZip2.BlockSize: ConvertibleFromString {
-
-    public static func convert(from: String) -> BZip2.BlockSize? {
-        guard let num = Int(from)
-            else { return nil }
-        return BZip2.BlockSize(rawValue: num)
-    }
-
-}