Revert "[BitCode] decode nossp fn attr"

This reverts commit 0b11d018cc2f2c6bea5dac8dc72140cdb502ca02.

Going with a simpler approach.

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1537,8 +1537,6 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::ByRef;
   case bitc::ATTR_KIND_MUSTPROGRESS:
     return Attribute::MustProgress;
-  case bitc::ATTR_KIND_NO_STACK_PROTECT:
-    return Attribute::NoStackProtect;
   }
 }