[python][rfc] Remove unused value_object attribute `owned_by_gdb'.

[Tom Tromey]

>>>>> "Thiago" == Thiago Jung Bauermann <bauerman@br.ibm.com> writes:

Thiago> I noticed that the owned_by_gdb element in value_object can only be set
Thiago> to 0 in the current code. Is this a remnant of some dropped effort? Any
Thiago> reason not to commit this patch?

Yeah, I think it is a remnant.  Please do zap it.

Related to this, the other day I finally realized what Daniel meant
when he said that reference counting struct value would not be hard.
This would let us drop those calls to value_copy...

Tom