top: restore missing support for 'MEMGRAPH_OLD' define

top: restore missing support for 'MEMGRAPH_OLD' define

When support for graphs was refactored, in that commit
referenced below, the logic for our 'MEMGRAPH_OLD' was
lost while the #define itself remained in the .h file.

Faced with deleting the #define or restoring the logic
I chose the latter. Thus, if one wanted to be reminded
how overstated 'used' memory once was, it can be done.

Reference(s):
. Sep, 2022 - refactored graph support
commit 2d5b51d1a2aa19d077a2f3db5be187f982d70e70

Signed-off-by: Jim Warner <james.warner@comcast.net>