Drop FXSYS_ from mem methods

This Cl drops the FXSYS_ from mem methods which are the same on all
platforms.

Bug: pdfium:694
Change-Id: I9d5ae905997dbaaec5aa0b2ae4c07358ed9c6236
Reviewed-on: https://pdfium-review.googlesource.com/3613
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/fpdf_structtree.cpp b/fpdfsdk/fpdf_structtree.cpp
index 5a922a1..06713fb 100644
--- a/fpdfsdk/fpdf_structtree.cpp
+++ b/fpdfsdk/fpdf_structtree.cpp
@@ -68,7 +68,7 @@
   CFX_ByteString encodedStr = str.UTF16LE_Encode();
   const unsigned long len = encodedStr.GetLength();
   if (buffer && len <= buflen)
-    FXSYS_memcpy(buffer, encodedStr.c_str(), len);
+    memcpy(buffer, encodedStr.c_str(), len);
   return len;
 }