[SymbolFile] Remove the SymbolContext parameter from FindNamespace.

Every callsite was passing an empty SymbolContext, so this parameter
had no effect.  Inside the DWARF implementation of this function,
however, there was one codepath that checked members of the
SymbolContext.  Since no call-sites actually ever used this
functionality, it was essentially dead code, so I've deleted this
code path as well.

llvm-svn: 351132
diff --git a/lldb/tools/lldb-test/lldb-test.cpp b/lldb/tools/lldb-test/lldb-test.cpp
index 29dd7cb..92c1780 100644
--- a/lldb/tools/lldb-test/lldb-test.cpp
+++ b/lldb/tools/lldb-test/lldb-test.cpp
@@ -441,9 +441,8 @@
   CompilerDeclContext *ContextPtr =
       ContextOr->IsValid() ? &*ContextOr : nullptr;
 
-  SymbolContext SC;
   CompilerDeclContext Result =
-      Vendor.FindNamespace(SC, ConstString(Name), ContextPtr);
+      Vendor.FindNamespace(ConstString(Name), ContextPtr);
   if (Result)
     outs() << "Found namespace: "
            << Result.GetScopeQualifiedName().GetStringRef() << "\n";