NFC: Simplify and clean up some existing tests for the versioned variants of #if canImport().

The ClangImporter tests for `#if canImport(..., _underlyingVersion: ...)` do not really depend on a Swift overlay being present for Simple.framework, so remove the overlay related `RUN` steps.

Author: tshortli

test/ClangImporter/can_import_underlying_version.swift

@@ -1,16 +1,12 @@
 // REQUIRES: VENDOR=apple
 // RUN: %empty-directory(%t)
-// RUN: %empty-directory(%t/overlaydir)
 // RUN: %empty-directory(%t/frameworks)
 
 // RUN: cp -rf %S/Inputs/frameworks/Simple.framework %t/frameworks/
 
 // RUN: echo "current-version: 1830.100" > %t/frameworks/Simple.framework/Simple.tbd
-// RUN: echo "@_exported import Simple" > %t.overlay.swift
-// RUN: echo "public func additional() {}" >> %t.overlay.swift
 
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -disable-implicit-concurrency-module-import -module-name Simple -F %t/frameworks/ %t.overlay.swift -emit-module-path %t/overlaydir/Simple.swiftmodule
-// RUN: %target-typecheck-verify-swift -disable-implicit-concurrency-module-import -I %t/overlaydir/ -F %t/frameworks
+// RUN: %target-typecheck-verify-swift -disable-implicit-concurrency-module-import -F %t/frameworks
 
 import Simple
 

test/ClangImporter/can_import_underlying_version_tbd_missing_version.swift

@@ -1,20 +1,16 @@
 // REQUIRES: VENDOR=apple
 // RUN: %empty-directory(%t)
-// RUN: %empty-directory(%t/overlaydir)
 // RUN: %empty-directory(%t/frameworks)
 
 // RUN: cp -rf %S/Inputs/frameworks/Simple.framework %t/frameworks/
 
 // RUN: echo "" > %t/frameworks/Simple.framework/Simple.tbd
-// RUN: echo "@_exported import Simple" > %t.overlay.swift
-// RUN: echo "public func additional() {}" >> %t.overlay.swift
-
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-objc-interop -disable-implicit-concurrency-module-import -module-name Simple -F %t/frameworks/ %t.overlay.swift -emit-module-path %t/overlaydir/Simple.swiftmodule
-// RUN: %target-typecheck-verify-swift -disable-implicit-concurrency-module-import -I %t/overlaydir/ -F %t/frameworks
+// RUN: %target-typecheck-verify-swift -disable-implicit-concurrency-module-import -F %t/frameworks
 
 import Simple
 
 func canImportVersioned() {
 #if canImport(Simple, _underlyingVersion: 3.3) // expected-warning {{cannot find user version number for Clang module 'Simple'; version number ignored}}
+  let a = 1  // expected-warning {{initialization of immutable value 'a' was never used; consider replacing with assignment to '_' or removing it}}
 #endif
 }

test/Parse/ConditionalCompilation/can_import_version.swift

@@ -1,7 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %empty-directory(%t/textual)
 // RUN: %empty-directory(%t/binary)
-// RUN: %empty-directory(%t/module-cache)
 
 // RUN: echo "public func foo() {}" > %t/Foo.swift
 // RUN: %target-swift-frontend -emit-module %t/Foo.swift -module-name Foo -swift-version 5 -disable-implicit-concurrency-module-import -user-module-version 113.330.1.2.3 -emit-module-interface-path %t/textual/Foo.swiftinterface -enable-library-evolution -emit-module-path %t/binary/Foo.swiftmodule
@@ -86,6 +85,7 @@ func canImportVersioned() {
 #endif
 }
 
+/// Test versions specified as string literals.
 func canImportVersionedString() {
 #if canImport(Foo, _version: "0")
   let majorZero = 1 // expected-warning {{initialization of immutable value 'majorZero' was never used; consider replacing with assignment to '_' or removing it}}
@@ -143,7 +143,7 @@ func canImportVersionedString() {
   let extraComponent = 1 // expected-warning {{initialization of immutable value 'extraComponent' was never used; consider replacing with assignment to '_' or removing it}}
 #endif
 
-#if canImport(Foo, _underlyingVersion: 113.33)
+#if canImport(Foo, _underlyingVersion: "113.33")
   // Foo is a Swift module with no underlying clang module.
   let underlyingMinorSmaller = 1
 #endif