Make "digdelv" system test work with BusyBox sed

Make "digdelv" system test work with BusyBox sed

The BusyBox version of sed treats leading '\+' in a regular expression
to be matched as a syntax error ("Repetition not preceded by valid
expression"), which triggers false positives for the "digdelv" system
test.  Make the relevant sed invocations work portably across all sed
implementations by removing the leading backslash.

(cherry picked from commit 266e3ed52a4bcda2a8e7815ffbbbe166516ec194)