Fix build of pdfium_fuzzer and pdfium_xfa_fuzzer on Windows

Remove declaration of unused and unitialized variable "wpath",
which caused compilation failure.

Bug: 891867
Change-Id: Icea7336c31d3897b72323b646a97899c5c2b66d0
Reviewed-on: https://chromium-review.googlesource.com/c/1259827
Commit-Queue: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596716}

pdf/pdfium/fuzzers/pdfium_fuzzer_helper.cc

@@ -86,7 +86,6 @@ std::string ProgramPath() {
   std::string result;
 
 #ifdef _WIN32
-  wchar_t wpath[MAX_PATH];
   char path[MAX_PATH];
   DWORD len = GetModuleFileNameA(NULL, path, MAX_PATH);
   if (len != 0)