Remove unused MadviseState hints

The only MadviseState enum value that is used is MadviseStateAtLoad.
Remove the enum entirely in favor of explicit load semantics for the
OatDexFile::MadviseDexFile call.

Follow-up work will address some of the existing madvise behavior for
low-RAM devices, particularly as it relates to the more recently added
madvise knobs like dalvik.vm.madvise.vdexfile.size.

Bug: 196052575
Test: test-art-host
Change-Id: I88211efce9193dc4c45274957898ce7b94eb330c
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 5e6ae1a..314aa29 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -1280,7 +1280,7 @@
                            std::make_move_iterator(dex_files.end()));
   }
   for (const std::unique_ptr<const DexFile>& dex_file : boot_dex_files_) {
-    OatDexFile::MadviseDexFile(*dex_file, MadviseState::kMadviseStateAtLoad);
+    OatDexFile::MadviseDexFileAtLoad(*dex_file);
   }
   InitializeObjectVirtualMethodHashes(GetClassRoot<mirror::Object>(this),
                                       image_pointer_size_,