C++ namespace cleanup (except tests).

libsolidity/ast/ASTUtils.h

@@ -17,14 +17,13 @@
 
 #pragma once
 
-namespace dev
-{
-namespace solidity
+namespace solidity::frontend
 {
 
+class VariableDeclaration;
+
 /// Find the topmost referenced variable declaration when the given variable
 /// declaration value is an identifier. Works only for constant variable declarations.
 VariableDeclaration const* rootVariableDeclaration(VariableDeclaration const& _varDecl);
 
 }
-}