MCObjectStreamer: Remove an unneeded getBackendPtr test

Summary:
All of `MCAsmBackend`, `MCCodeEmitter`, and `MCObjectWriter` must be
non-null.

Test Plan: 

Reviewers: 

Subscribers: 

Tasks: 

Tags: 


Differential Revision: https://phabricator.intern.facebook.com/D60251105

Author: MaskRay

llvm/lib/MC/MCObjectStreamer.cpp

@@ -32,8 +32,8 @@ MCObjectStreamer::MCObjectStreamer(MCContext &Context,
       Assembler(std::make_unique<MCAssembler>(
           Context, std::move(TAB), std::move(Emitter), std::move(OW))),
       EmitEHFrame(true), EmitDebugFrame(false) {
-  if (Assembler->getBackendPtr())
-    setAllowAutoPadding(Assembler->getBackend().allowAutoPadding());
+  assert(Assembler->getBackendPtr() && Assembler->getEmitterPtr());
+  setAllowAutoPadding(Assembler->getBackend().allowAutoPadding());
   if (Context.getTargetOptions() && Context.getTargetOptions()->MCRelaxAll)
     Assembler->setRelaxAll(true);
 }