[memprof][NFC] Update a stale comment about symbolization.

[snehasish]

Summary

Symbolization of position independent code was added in D146181. Update
the comment to note that the checks below are to sanity check the
assumptions we make to simplify symbolization.

[davidxl]

lgtm

[tejohnson]

lgtm

llvm/lib/ProfileData/RawMemProfReader.cpp

Error RawMemProfReader::initialize(std::unique_ptr<MemoryBuffer> DataBuffer) {
   auto *ElfObject = dyn_cast<object::ELFObjectFileBase>(Binary.getBinary());
   if (!ElfObject) {
     return report(make_error<StringError>(Twine("Not an ELF file: "),
                                           inconvertibleErrorCode()),
                   FileName);
   }
 
   // Check whether the profiled binary was built with position independent code
-  // (PIC). For now we provide a error message until symbolization support
-  // is added for pic.
+  // (PIC). Perform sanity checks for assumptions we rely on to simplify
+  // symbolization.
   auto* Elf64LEObject = llvm::cast<llvm::object::ELF64LEObjectFile>(ElfObject);
   const llvm::object::ELF64LEFile& ElfFile = Elf64LEObject->getELFFile();
   auto PHdrsOr = ElfFile.program_headers();
   if (!PHdrsOr)
     return report(
         make_error<StringError>(Twine("Could not read program headers: "),
                                 inconvertibleErrorCode()),
         FileName);