Remove triple from SwiftBuild system output path

The triple name in the SwiftBuild build system is redundant.  Remove the
triple from the output path.

Author: bkhouri

Sources/SPMBuildCore/Triple+Extensions.swift

@@ -32,7 +32,9 @@ extension Triple {
             // can be used to build for any Apple platform and it has its own
             // conventions for build subpaths based on platforms.
             return "apple"
-        case .swiftbuild, .native:
+        case .swiftbuild:
+            return ""
+        case .native:
             return self.platformBuildPathComponent
         }
     }

Sources/_InternalTestSupport/BuildSystemProvider+Configuration.swift

@@ -66,7 +66,7 @@ extension BuildSystemProvider.Kind {
         case .native:
             return scratchPath + [tripleString, "\(config)".lowercased()]
         case .swiftbuild:
-            return scratchPath + [tripleString, "Products", "\(config)".capitalized + suffix]
+            return scratchPath + ["Products", "\(config)".capitalized + suffix]
         case .xcode:
             return scratchPath + ["apple", "Products", "\(config)".capitalized + suffix]
         }