[ELF] - Move LinkerScript::discard to LinkerScriptBase. NFC.

Became possible after r297844

llvm-svn: 297848
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 5f2c9a1..fc56c5f 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -288,11 +288,10 @@
   }
 }
 
-template <class ELFT>
-void LinkerScript<ELFT>::discard(ArrayRef<InputSectionBase *> V) {
+void LinkerScriptBase::discard(ArrayRef<InputSectionBase *> V) {
   for (InputSectionBase *S : V) {
     S->Live = false;
-    if (S == In<ELFT>::ShStrTab)
+    if (S == InX::ShStrTab)
       error("discarding .shstrtab section is not allowed");
     discard(S->DependentSections);
   }