[clangd][unittests][IncludeCleaner] Don't call findReferencedFiles() if the result is not used

[ArcsinX]

Summary

IncludeCleaner.RecursiveInclusion and IncludeCleaner.IWYUPragmaExport tests don't check referenced files list, so we don't need to call findReferencedFiles() there.

clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp

TU.AdditionalFiles["foo.h"] = R"cpp(
 
     #endif
   )cpp";
   TU.AdditionalFiles["bar.h"] = guard(R"cpp(
     #include "foo.h"
   )cpp");
   ParsedAST AST = TU.build();
 
-  auto ReferencedFiles = findReferencedFiles(
-      findReferencedLocations(AST), AST.getIncludeStructure(),
-      AST.getCanonicalIncludes(), AST.getSourceManager());
   EXPECT_THAT(AST.getDiagnostics(), llvm::ValueIs(IsEmpty()));
   EXPECT_THAT(computeUnusedIncludes(AST), IsEmpty());
 }
 
 TEST(IncludeCleaner, IWYUPragmaExport) {
   TestTU TU;
   TU.Code = R"cpp(
     #include "foo.h"
     )cpp";
   TU.AdditionalFiles["foo.h"] = R"cpp(
     #ifndef FOO_H
     #define FOO_H
 
     #include "bar.h" // IWYU pragma: export
 
     #endif
   )cpp";
   TU.AdditionalFiles["bar.h"] = guard(R"cpp(
     void bar() {}
   )cpp");
   ParsedAST AST = TU.build();
 
-  auto ReferencedFiles = findReferencedFiles(
-      findReferencedLocations(AST), AST.getIncludeStructure(),
-      AST.getCanonicalIncludes(), AST.getSourceManager());
   EXPECT_THAT(AST.getDiagnostics(), llvm::ValueIs(IsEmpty()));
   // FIXME: This is not correct: foo.h is unused but is not diagnosed as such
   // because we ignore headers with IWYU export pragmas for now.
   EXPECT_THAT(computeUnusedIncludes(AST), IsEmpty());
 }
 
 } // namespace
 } // namespace clangd
 } // namespace clang