Remove the downgrade 4.1.2 -> 4.0.18 patch accidentally merged from 4.0 to 4.1; the patch must NOT be merged to 4.1; this fixes Bug #2883


innobase/trx/trx0sys.c:
  Remove the downgrade 4.1.2 -> 4.0.18 patch accidentally merged from 4.0 to 4.1; the patch must NOT be merged to 4.1; this fixes Bug #2883