Clean up unnecessary use of TString

TString was being used in some places where it was not really needed.
Clean these up.

BUG=angleproject:2267
TEST=angle_unittests

Change-Id: Ib7fd26f9c6b6b885433c840a9520393908f1f902
Reviewed-on: https://chromium-review.googlesource.com/887068
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/compiler/translator/UseInterfaceBlockFields.cpp b/src/compiler/translator/UseInterfaceBlockFields.cpp
index df0c2f9..900119d 100644
--- a/src/compiler/translator/UseInterfaceBlockFields.cpp
+++ b/src/compiler/translator/UseInterfaceBlockFields.cpp
@@ -43,7 +43,7 @@
                            TIntermSequence *sequence,
                            const TSymbolTable &symbolTable)
 {
-    ASSERT(var.name.find_last_of('[') == TString::npos);
+    ASSERT(var.name.find_last_of('[') == std::string::npos);
     TIntermSymbol *symbol = ReferenceGlobalVariable(ImmutableString(var.name), symbolTable);
     AddNodeUseStatements(symbol, sequence);
 }