t4216: use an '&&'-chain

In a759bfa9ee (t4216: add end to end tests for git log with Bloom filters, 2020-04-06), a 'rm' invocation was added without a corresponding '&&' chain. When 'trace.perf' already exists, everything works fine. However, the function can be executed without 'trace.perf' on disk (eg., when the subset of tests run is altered with '--run'), and so the bare 'rm' complains about a missing file. To remove some noise from the test log, invoke 'rm' with '-f', at which point it is sensible to place the 'rm -f' in an '&&'-chain, which is both (1) our usual style, and (2) avoids a broken chain in the future if more commands are added at the beginning of the function. Helped-by: Eric Sunshine <sunshine@sunshineco.com> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>