Revert "Adding constructor of CFX_ByteString that takes a std::ostringstream."

This reverts commit 4633d52736c4b926eceb1e18c4b379ff57fd31fa.

Reason for revert: windows_xfa_clang broke?

Original change's description:
> Adding constructor of CFX_ByteString that takes a std::ostringstream.
> 
> Bug: pdfium:731
> Change-Id: Ia0734deb3f309732dccae5c0cf6131d32713e87a
> Reviewed-on: https://pdfium-review.googlesource.com/6394
> Reviewed-by: dsinclair <dsinclair@chromium.org>
> Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>

TBR=dsinclair@chromium.org,hnakashima@chromium.org
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: pdfium:731

Change-Id: I674aa1be12d6777c4d565d3131910ac5a11d8dc0
Reviewed-on: https://pdfium-review.googlesource.com/6395
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
diff --git a/core/fxcrt/cfx_bytestring.cpp b/core/fxcrt/cfx_bytestring.cpp
index b83c59f..f0dc370 100644
--- a/core/fxcrt/cfx_bytestring.cpp
+++ b/core/fxcrt/cfx_bytestring.cpp
@@ -189,10 +189,6 @@
   }
 }
 
-CFX_ByteString::CFX_ByteString(std::ostringstream& outStream)
-    : CFX_ByteString(outStream.str().c_str(),
-                     static_cast<int>(outStream.tellp())) {}
-
 CFX_ByteString::~CFX_ByteString() {}
 
 const CFX_ByteString& CFX_ByteString::operator=(const char* pStr) {
diff --git a/core/fxcrt/cfx_bytestring.h b/core/fxcrt/cfx_bytestring.h
index 23e0249..c4d4895 100644
--- a/core/fxcrt/cfx_bytestring.h
+++ b/core/fxcrt/cfx_bytestring.h
@@ -8,7 +8,6 @@
 #define CORE_FXCRT_CFX_BYTESTRING_H_
 
 #include <functional>
-#include <sstream>
 #include <utility>
 
 #include "core/fxcrt/cfx_retain_ptr.h"
@@ -46,7 +45,6 @@
   explicit CFX_ByteString(const CFX_ByteStringC& bstrc);
   CFX_ByteString(const CFX_ByteStringC& bstrc1, const CFX_ByteStringC& bstrc2);
   CFX_ByteString(const std::initializer_list<CFX_ByteStringC>& list);
-  explicit CFX_ByteString(std::ostringstream& outStream);
 
   ~CFX_ByteString();