Remove FXSYS_strlen and FXSYS_wcslen

With the conversion of internal string sizes to size_t, these wrappers
are no longer needed. Replacing them with strlen and wcslen
respectively.

BUG=pdfium:828

Change-Id: Ia087ca2ddaf688a57ec9bd9ddfb8533cbe41510d
Reviewed-on: https://pdfium-review.googlesource.com/14890
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/javascript/Field.cpp b/fpdfsdk/javascript/Field.cpp
index fa5d478..a89df16 100644
--- a/fpdfsdk/javascript/Field.cpp
+++ b/fpdfsdk/javascript/Field.cpp
@@ -2610,8 +2610,7 @@
           iIndex = pFormField->GetSelectedIndex(i);
           ElementValue =
               CJS_Value(pRuntime, pFormField->GetOptionValue(iIndex).c_str());
-          if (FXSYS_wcslen(ElementValue.ToCFXWideString(pRuntime).c_str()) ==
-              0) {
+          if (wcslen(ElementValue.ToCFXWideString(pRuntime).c_str()) == 0) {
             ElementValue =
                 CJS_Value(pRuntime, pFormField->GetOptionLabel(iIndex).c_str());
           }