Fix deletion using assigning empty against arrays

[itchyny]

This pull request fixes #2051, by delaying path deletions. Also fixes #2397, fixes #2422 and fixes #2440.

 % ./jq -c '(.[] | select(. >= 2)) |= empty' <<< '[1,5,3,0,7]'
[1,0]
 % ./jq -c '.[] |= select(. >= 4)' <<< '[1,5,3,0,7]'
[5,7]
 % ./jq -c '.[] |= select(. == 2)' <<< '[1,5,3,0,7]'
[]

[coveralls]

Coverage remained the same at 84.134% when pulling d452f7d on itchyny:fix-modify-array-empty into 6306ac8 on stedolan:master.

[nicowilliams]

Thank you!