Remove extraneous ')' in abstract.h (GH-19146)

Author: Jimmy Yang

Include/object.h

@@ -27,7 +27,7 @@ of data it contains.  An object's type is fixed when it is created.
 Types themselves are represented as objects; an object contains a
 pointer to the corresponding type object.  The type itself has a type
 pointer pointing to the object representing the type 'type', which
-contains a pointer to itself!).
+contains a pointer to itself!.
 
 Objects do not float around in memory; once allocated an object keeps
 the same size and address.  Objects that must hold variable-size data