De-template SyntheticSection.

This class didn't use ELFT.

llvm-svn: 296313
diff --git a/lld/ELF/OutputSections.cpp b/lld/ELF/OutputSections.cpp
index 89bc440..39b2fe0 100644
--- a/lld/ELF/OutputSections.cpp
+++ b/lld/ELF/OutputSections.cpp
@@ -137,7 +137,7 @@
     return;
 
   InputSection *First = Sections[0];
-  if (isa<SyntheticSection<ELFT>>(First))
+  if (isa<SyntheticSection>(First))
     return;
 
   this->Link = In<ELFT>::SymTab->OutSec->SectionIndex;