go/zodb/fs1: Remove old testdata files

We recently modrnized FileStorage/go tests to have all ZODB kinds of
data which live in testdata/<zkind>/ for example testdata/py2_pickle3/ -
see recent patch "go/zodb/fs1: Test FileStorage on all py2/py3 ZODB
kinds of data we care about".

We also updated all other packages to use that new FileStorage testdata.

-> Now is the time for old testdata to go.

go/zodb/storage/fs1/testdata/empty.fs

-FS21
\ No newline at end of file