Decrease the Series_Memory when the series is freed
Decrease the Series_Memory when the series is freed

Or this stat doesn't make much sense. With this change, it now refers to
the series memory that's in use.

zsx/r3,zsx/r3,zsx/r3,Pointillistic/rebol-lang,Pointillistic/rebol-lang,zsx/r3,Pointillistic/rebol-lang,Pointillistic/rebol-lang