De-template SyntheticSection.

This class didn't use ELFT.

llvm-svn: 296313
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 3b045f0..04df93b 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -490,7 +490,7 @@
     // empty ones afterwards (because there is no way to know whether they were
     // going be empty or not other than actually running linker scripts.)
     // We need to ignore remains of empty sections.
-    if (auto *Sec = dyn_cast<SyntheticSection<ELFT>>(ID))
+    if (auto *Sec = dyn_cast<SyntheticSection>(ID))
       if (Sec->empty())
         continue;