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.

bin/tests/system/digdelv/tests.sh

@@ -59,8 +59,8 @@ delv_with_opts() {
 }
 
 KEYID="$(cat ns2/keyid)"
-KEYDATA="$(< ns2/keydata sed -e 's/\+/[+]/g')"
-NOSPLIT="$(< ns2/keydata sed -e 's/\+/[+]/g' -e 's/ //g')"
+KEYDATA="$(< ns2/keydata sed -e 's/+/[+]/g')"
+NOSPLIT="$(< ns2/keydata sed -e 's/+/[+]/g' -e 's/ //g')"
 
 if [ -x "$DIG" ] ; then
   n=$((n+1))