Remove clang detected warning on tautological comparison

Bug: 16903117

(cherry picked from commit c991107a90698012c2b0babc030b8ab85491d1e3)

Change-Id: I94d36d8d26d4090b4c2ad128fde9dab2b1173533
diff --git a/runtime/dex_file.cc b/runtime/dex_file.cc
index e1a7771..ddc2147 100644
--- a/runtime/dex_file.cc
+++ b/runtime/dex_file.cc
@@ -386,7 +386,6 @@
 }
 
 bool DexFile::CheckMagicAndVersion(std::string* error_msg) const {
-  CHECK(header_->magic_ != NULL) << GetLocation();
   if (!IsMagicValid(header_->magic_)) {
     std::ostringstream oss;
     oss << "Unrecognized magic number in "  << GetLocation() << ":"