Revert "Introduce a string_ostream string builder facilty"

Temporarily back out commits r211749, r211752 and r211754.

llvm-svn: 211814
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 3f9eb07..7840342 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -281,7 +281,8 @@
   unsigned RelaxedOp = getRelaxedOpcode(Inst.getOpcode());
 
   if (RelaxedOp == Inst.getOpcode()) {
-    small_string_ostream<256> OS;
+    SmallString<256> Tmp;
+    raw_svector_ostream OS(Tmp);
     Inst.dump_pretty(OS);
     OS << "\n";
     report_fatal_error("unexpected instruction to relax: " + OS.str());