Fixup some grammar.

This Cl updates some double negative grammar to be a bit more readable.

Change-Id: Id5d9c64acc1dd8422b8116d8a6c1bf149f99e592
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/103260
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/src/tint/resolver/resolver.cc b/src/tint/resolver/resolver.cc
index 911b66c..d57be4c 100644
--- a/src/tint/resolver/resolver.cc
+++ b/src/tint/resolver/resolver.cc
@@ -2280,7 +2280,7 @@
             // Note: The spec is currently vague around the rules here. See
             // https://github.com/gpuweb/gpuweb/issues/3081. Remove this comment when resolved.
             std::string desc = "var '" + builder_->Symbols().NameFor(symbol) + "' ";
-            AddError(desc + "cannot not be referenced at module-scope", expr->source);
+            AddError(desc + "cannot be referenced at module-scope", expr->source);
             AddNote(desc + "declared here", variable->Declaration()->source);
             return nullptr;
         }