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

(cherry picked from commit ac2cfe6)

Co-authored-by: Jimmy Yang <[email protected]>

Author: miss-islington

Include/object.h

@@ -26,7 +26,7 @@ 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