C++: Remove initialization of enum variable in DesignatorAST

The tool 'cplusplus-update-frontend' can't handle that and thus will
rewrite that class without this initialization.

The member is properly initialized at use.

Change-Id: I2c8c57be47b5fe953c2518254656e5e38ba90f08
Reviewed-by: Wang Hoi <wanghoi@126.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/libs/3rdparty/cplusplus/AST.h

@@ -4556,7 +4556,6 @@ public:
 
 public:
     DesignatorAST()
-        : type(Invalid)
     {}
 
     virtual DesignatorAST *asDesignator() { return this; }