[Support] Remove a redundant constructor in SubsectionAndTagToTagName (NFC) (#164118)

This patch simplifies the struct by switching to C++ aggregate
initialization.

Author: kazutakahirata

llvm/include/llvm/Support/ELFAttributes.h

@@ -48,8 +48,6 @@ struct SubsectionAndTagToTagName {
   StringRef SubsectionName;
   unsigned Tag;
   StringRef TagName;
-  SubsectionAndTagToTagName(StringRef SN, unsigned Tg, StringRef TN)
-      : SubsectionName(SN), Tag(Tg), TagName(TN) {}
 };
 
 namespace ELFAttrs {