t2028: tighten grep expression to make "move worktree" test more robust

Following a rename of worktree "source" to "destination", the "move worktree" test uses grep to verify that the output of "git worktree list --porcelain" does not contain "source" (and does contain "destination"). Unfortunately, the grep expression is too loose and can match unexpectedly. For example, if component of the test trash directory path matches "source" (e.g. "/home/me/sources/git/t/trash*"), then the test will be fooled into thinking that "source" still exists. Tighten the expression to avoid such accidental matches. While at it, drop an unused variable ("toplevel") from the test and tighten a similarly too-loose expression in a related test. Reported-by: Jens Krüger <Jens.Krueger@frm2.tum.de> Signed-off-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>