[ELF] Delete a redundant assignment to SectionBase::assigned. NFC

LinkerScript::discard marks a section dead. It is unnecessary to set the
`assigned` bit.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@371804 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/ELF/LinkerScript.cpp b/ELF/LinkerScript.cpp
index dbf705d..8d8f3b5 100644
--- a/ELF/LinkerScript.cpp
+++ b/ELF/LinkerScript.cpp
@@ -457,7 +457,6 @@
     if (s == mainPart->hashTab)
       mainPart->hashTab = nullptr;
 
-    s->assigned = false;
     s->markDead();
     discard(s->dependentSections);
   }