rmdel removes the delta specified by the SCCS delta ID (SID)
supplied with -r. The delta to be removed must be the most
recent (leaf) delta in its branch. In addition, the SID must not be that of a version checked
out for editing: it must not appear in any entry of the version lock file
If you created the delta, or, if you own the file and directory and
have write permission, you can remove it with rmdel.
If a directory name is used in place of the s.filename argument, the rmdel command applies to
all s.files in that directory. Unreadable s.files produce an error; processing continues with the next file
(if any). The use of `-' as the s.filename argument indicates that the names of files are to be read
from the standard input, one s.file per line.