[PATCH] gdbserver: add client_state destructor

[Tom Tromey]

>> At some point we went through the tree and removed all these IIRC.

Guinevere> I think I have a case of friday brains. You mean removed all nullptr
Guinevere> checks, or removed unnecessary xfrees?

Sorry.  All the checks of null before free were removed at some point.

Though I see that gdb-xfree.h still does the check.  Lol.
IIRC, the gnulib folks looked into this and concluded that no existing
system requires the check before a call to free.

Tom