Revert "HACK: Disable tests that require @testable import."

This reverts commit 10b7b0e.

Author: artemcm

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -12,8 +12,6 @@
 import XCTest
 import TSCBasic
 
-#if false
-// FIXME: Disabled due to @testable import
 @testable import SwiftDriver
 
 final class NonincrementalCompilationTests: XCTestCase {
@@ -618,4 +616,3 @@ final class IncrementalCompilationTests: XCTestCase {
     try! localFileSystem.writeFileContents(dst, bytes: ByteString(d))
   }
 }
-#endif

Tests/SwiftDriverTests/ModuleDependencyGraphTests.swift

@@ -11,9 +11,6 @@
 //===----------------------------------------------------------------------===//
 
 import XCTest
-
-#if false
-// FIXME: Disabled due to @testable import
 @testable import SwiftDriver
 import TSCBasic
 
@@ -1368,4 +1365,3 @@ fileprivate extension Set where Element == ExternalDependency {
     contains(s.asExternal)
   }
 }
-#endif

Tests/SwiftDriverTests/TwoDMapTests.swift

@@ -10,9 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if false
 import XCTest
-// FIXME: Disabled due to testable import
 @testable import SwiftDriver
 
 class TwoDMapTests: XCTestCase {
@@ -108,4 +106,3 @@ class TwoDMapTests: XCTestCase {
   }
 
 }
-#endif