Remove old fields that have been deprecated since before 1.100

tasks.Mailer          from,subject,failureOnly,charset 1.10
model.Project         slave                            1.60
model.Descriptor      properties                       1.62
model.Slave           command,localFS                  1.69
model.AbstractProject enableRemoteTrigger              1.77
model.FingerprintMap  core                             1.91
If anyone still has very old XML with these, OldDataMonitor will
still handle it (as unreadable data instead of old data, and
with a bit more noise in the log).