Revert "Add implicit null and stack checks for x86"

It breaks cross compilation with x86_64.

This reverts commit 34e826ccc80dc1cf7c4c045de6b7f8360d504ccf.

Change-Id: I34ba07821fc0a022fda33a7ae21850957bbec5e7
diff --git a/compiler/dex/quick/gen_common.cc b/compiler/dex/quick/gen_common.cc
index 0bb253c..b31e9a2 100644
--- a/compiler/dex/quick/gen_common.cc
+++ b/compiler/dex/quick/gen_common.cc
@@ -195,7 +195,6 @@
     if (!(cu_->disable_opt & (1 << kNullCheckElimination)) && (opt_flags & MIR_IGNORE_NULL_CHECK)) {
       return;
     }
-    // Insert after last instruction.
     MarkSafepointPC(last_lir_insn_);
   }
 }
@@ -623,7 +622,7 @@
         LockTemp(r_tmp);
         LIR* uninit_branch = OpCmpMemImmBranch(kCondLt, r_tmp, r_base,
                                           mirror::Class::StatusOffset().Int32Value(),
-                                          mirror::Class::kStatusInitialized, nullptr, nullptr);
+                                          mirror::Class::kStatusInitialized, NULL);
         LIR* cont = NewLIR0(kPseudoTargetLabel);
 
         AddSlowPath(new (arena_) StaticFieldSlowPath(this, unresolved_branch, uninit_branch, cont,
@@ -716,7 +715,7 @@
         LockTemp(r_tmp);
         LIR* uninit_branch = OpCmpMemImmBranch(kCondLt, r_tmp, r_base,
                                           mirror::Class::StatusOffset().Int32Value(),
-                                          mirror::Class::kStatusInitialized, nullptr, nullptr);
+                                          mirror::Class::kStatusInitialized, NULL);
         LIR* cont = NewLIR0(kPseudoTargetLabel);
 
         AddSlowPath(new (arena_) StaticFieldSlowPath(this, unresolved_branch, uninit_branch, cont,