[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/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
index 698de0e..fa839d5 100644
--- a/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
+++ b/lldb/source/Plugins/SymbolFile/NativePDB/SymbolFileNativePDB.cpp
@@ -1550,8 +1550,7 @@
 }
 
 CompilerDeclContext
-SymbolFileNativePDB::FindNamespace(const SymbolContext &sc,
-                                   const ConstString &name,
+SymbolFileNativePDB::FindNamespace(const ConstString &name,
                                    const CompilerDeclContext *parent_decl_ctx) {
   return {};
 }