test_all: run the bisync integration tests on TestS3Rclone

Before this change, `cmd/bisync` was excluded on `TestS3Rclone`
(`rclone serve s3`), one of the backends `108504963` excluded because the
tests always failed there at the time. After this change, they run there
again: with `test_all` on Linux, every case passes or skips, with or
without the preceding changes to the test harness.

fstest/test_all/config.yaml

@@ -272,7 +272,6 @@ backends:
    remote:   "TestS3Rclone:"
    fastlist: true
    ignoretests:
-     - cmd/bisync
      - cmd/gitannex
  - backend:  "s3"
    remote:   "TestS3Minio:"