Revert "IRGen: address a TODO in the type metadata emission"

This reverts commit b9066c9. It is still triggering relocation-
related errors on some CI configurations.

Author: jckarter

lib/IRGen/GenMeta.cpp

@@ -1989,16 +1989,11 @@ llvm::Value *IRGenFunction::emitTypeLayoutRef(SILType type) {
 
 void IRGenModule::setTrueConstGlobal(llvm::GlobalVariable *var) {
   switch (TargetInfo.OutputObjectFormat) {
-  case llvm::Triple::UnknownObjectFormat:
-    llvm_unreachable("unknown object format");
   case llvm::Triple::MachO:
-    var->setSection("__TEXT,__const");
+    var->setSection("__TEXT, __const");
     break;
-  case llvm::Triple::ELF:
-    var->setSection(".rodata");
-    break;
-  case llvm::Triple::COFF:
-    var->setSection(".rdata");
+  // TODO: ELF?
+  default:
     break;
   }
 }