roachtest: delete synctest

This test has been skipped since May 2020, because Pebble code is written
to crash on an error when writing to the MANIFEST and the WAL, since it
is not viable to continue. Additionally, there were problems with hangs
due to charybdefs returning EAGAIN (which have since been fixed).

We are deleting this now since:
- The purpose of this test is to test that Pebble does not lose data due
  to filesystem errors. It does so in a cruder manner than Pebble's
  strict MemFS based testing (which came later). Given the existence of
  the latter, there is no good reason to retain this test.

- Working around charybdefs flakiness (see cockroachdb#102492), and Pebble's
  failstop-on-error behavior is not worth the initial and ongoing
  maintenance effort.

Epic: none

Fixes: cockroachdb#48603

Release note: None

pkg/cli/debug_synctest.go

@@ -30,6 +30,11 @@ import (
 	"github.com/spf13/cobra"
 )
 
+// TODO(sumeer): consider deleting this command, now that it is no longer
+// exercised by the synctest roachtest (which has been deleted). We will need
+// to confirm that users of CockroachDB are not running it as part of their
+// testing.
+
 var debugSyncTestCmd = &cobra.Command{
 	Use:   "synctest <empty-dir> <nemesis-script>",
 	Short: "Run a log-like workload that can help expose filesystem anomalies",

pkg/cmd/roachtest/tests/BUILD.bazel

@@ -152,7 +152,6 @@ go_library(
         "sqlsmith.go",
         "sstable_corruption.go",
         "status_server.go",
-        "synctest.go",
         "sysbench.go",
         "tlp.go",
         "tombstones.go",