Remove an obsolete comment in snapbuild.c

Hi all,

While reading the code I realized that the following comment of
SnapBuildOnDick is obsolete:

/*
 * We store current state of struct SnapBuild on disk in the following manner:
 *
 * struct SnapBuildOnDisk;
 * TransactionId * running.xcnt_space;
 * TransactionId * committed.xcnt; (*not xcnt_space*)
 *
 */
typedef struct SnapBuildOnDisk

Since SnapBuild has no longer "running" struct, it should be removed.
Please find an attached patch.

Regards,

-- 
Masahiko Sawada
EDB:  https://www.enterprisedb.com/