templatefilters: drop callable support from json()
This backs out ae5447de4c11. A callable should be evaluated beforehand
by templater.runsymbol().
fixbundle() {
grep -v 'saving bundle' | grep -v 'saved backup' | \
grep -v added | grep -v adding | \
grep -v "unable to find 'e' for patching" | \
grep -v "e: No such file or directory" | \
cat
}