Remove `SymbolFileDWARF *` when there is already `DWARFUnit *`

In D61502#1503247 @clayborg suggested that SymbolFileDWARF *dwarf2Data is
really redundant in all the calls with also having DWARFUnit *cu. So remove it.

One `SymbolFileDWARF *` nullptr check
(DWARFDebugInfoEntry::GetDIENamesAndRanges) could be removed, other two nullptr
checks (DWARFDebugInfoEntry::GetName and DWARFDebugInfoEntry::AppendTypeName)
need to stay in place (now for `DWARFUnit *`).

Differential Revision: https://reviews.llvm.org/D62011

llvm-svn: 361277
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index 66ad3ad..c713e24 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -1485,15 +1485,15 @@
   if (GetDebugMapSymfile())
     return nullptr;
 
-  const char *dwo_name = cu_die.GetAttributeValueAsString(
-      this, &dwarf_cu, DW_AT_GNU_dwo_name, nullptr);
+  const char *dwo_name =
+      cu_die.GetAttributeValueAsString(&dwarf_cu, DW_AT_GNU_dwo_name, nullptr);
   if (!dwo_name)
     return nullptr;
 
   SymbolFileDWARFDwp *dwp_symfile = GetDwpSymbolFile();
   if (dwp_symfile) {
-    uint64_t dwo_id = cu_die.GetAttributeValueAsUnsigned(this, &dwarf_cu,
-                                                         DW_AT_GNU_dwo_id, 0);
+    uint64_t dwo_id =
+        cu_die.GetAttributeValueAsUnsigned(&dwarf_cu, DW_AT_GNU_dwo_id, 0);
     std::unique_ptr<SymbolFileDWARFDwo> dwo_symfile =
         dwp_symfile->GetSymbolFileForDwoId(&dwarf_cu, dwo_id);
     if (dwo_symfile)
@@ -1503,8 +1503,8 @@
   FileSpec dwo_file(dwo_name);
   FileSystem::Instance().Resolve(dwo_file);
   if (dwo_file.IsRelative()) {
-    const char *comp_dir = cu_die.GetAttributeValueAsString(
-        this, &dwarf_cu, DW_AT_comp_dir, nullptr);
+    const char *comp_dir =
+        cu_die.GetAttributeValueAsString(&dwarf_cu, DW_AT_comp_dir, nullptr);
     if (!comp_dir)
       return nullptr;