Revert "cat-file: split --batch input lines on whitespace"

Revert "cat-file: split --batch input lines on whitespace"

This reverts commit c334b87b30c1464a1ab563fe1fb8de5eaf0e5bac; the
update assumed that people only used the command to read from
"rev-list --objects" output, whose lines begin with a 40-hex object
name followed by a whitespace, but it turns out that scripts feed
random extended SHA-1 expressions (e.g. "HEAD:$pathname") in which
a whitespace has to be kept.