Remove Sendable conformance on Bundle from SwiftPM

Foundation added this conformance on their side in `main` (swiftlang/swift-corelibs-foundation#4963) and `release/6.0` (swiftlang/swift-corelibs-foundation#4978).

rdar://129599679

Author: MaxDesiatov

Sources/Build/BuildDescription/SwiftTargetBuildDescription.swift

@@ -380,11 +380,6 @@ public final class SwiftTargetBuildDescription {
             """
             import Foundation
 
-            #if compiler(>=6.0)
-            extension Foundation.Bundle: @unchecked @retroactive Sendable {}
-            #else
-            extension Foundation.Bundle: @unchecked Sendable {}
-            #endif
             extension Foundation.Bundle {
                 static let module: Bundle = {
                     let mainPath = \(mainPathSubstitution)