Remove commented signing cert constant (#917)

Removes the commented signing cert constant
variable from the PAL header file. The
correct location for this constant is the
aws_ota_codesigner_certificate.h file.

FreeRTOS-Plus/Demo/AWS/Ota_Windows_Simulator/Common/Ota_PAL/Win32/ota_pal.h

@@ -34,8 +34,6 @@
 
 #include "ota.h"
 
-//static const char signingcredentialSIGNING_CERTIFICATE_PEM[] = "Paste code signing certificate here.";
-
 /**
  * @brief Abort an OTA transfer.
  *