Remove unused local in OpenSSLCertUtils

Summary: It's unused, and MSVC is warning about that fact.

Reviewed By: anirudhvr

Differential Revision: D4894403

fbshipit-source-id: 767b944eb9fa0376c795555357c09bbf9179e24f

folly/ssl/OpenSSLCertUtils.cpp

@@ -159,8 +159,6 @@ std::string OpenSSLCertUtils::getDateTimeStr(const ASN1_TIME* time) {
     return "";
   }
 
-  std::array<char, 32> buf;
-
   auto bio = BioUniquePtr(BIO_new(BIO_s_mem()));
   if (bio == nullptr) {
     throw std::runtime_error("Cannot allocate bio");