message: [Target] Remove unused swift headers
diff: #include <memory>
  #include <mutex>
  -#include "swift/Frontend/Frontend.h"
  -#include "swift/SIL/SILModule.h"
  -
  using namespace lldb;
  using namespace lldb_private;
  @@ -2487,7 +2484,7 @@ SwiftASTContextReader Target::GetScratchSwiftASTContext(
  ModuleLanguage idx = {lldb_module, lldb::eLanguageTypeSwift};
  auto cached = m_scratch_typesystem_for_module.find(idx);
  if (cached != m_scratch_typesystem_for_module.end()) {
  - auto *cached_ast_ctx = cast<SwiftASTContext>(cached->second.get());
  + auto *cached_ast_ctx = llvm::cast<SwiftASTContext>(cached->second.get());
  if (cached_ast_ctx->HasFatalErrors() &&
  !m_cant_make_scratch_type_system.count(lldb::eLanguageTypeSwift)) {
  DisplayFallbackSwiftContextErrors(cached_ast_ctx);
  @@ -2510,7 +2507,7 @@ SwiftASTContextReader Target::GetScratchSwiftASTContext(
  bool fallback = true;
  auto typesystem_sp = SwiftASTContext::CreateInstance(
  lldb::eLanguageTypeSwift, *lldb_module, this, fallback);
  - auto *swift_ast_ctx = cast<SwiftASTContext>(typesystem_sp.get());
  + auto *swift_ast_ctx = llvm::cast<SwiftASTContext>(typesystem_sp.get());
  m_scratch_typesystem_for_module.insert({idx, typesystem_sp});
  GetSwiftScratchContextLock().unlock();
  if (log)
  