dashboard: unmark known-issues with low failure rates

I had initially added known issues fairly aggressively in order to use
them to reduce noise in 'greplogs -triage'. Now that we are using
'watchflakes' for triage, that noise reduction is no longer important
(the failures are already clustered to their respective known issues),
and having greyed-out cells on the dashboard makes new regressions too
easy to miss.

Concretely:

- golang/go#42212 is mostly specific to x/net at this point (as
  golang/go#57841)

- There have been no failures matching golang/go#51001 since October.

- golang/go#52724 has been so rare lately that we hadn't yet added a
  'watchflakes' pattern for it.

- There have been no failures matching golang/go#51443 since May.

- There have been no failures matching golang/go#53116 or
  golang/go#53093 since I enabled 'watchflakes' for the builder in
  December.

- The linux-amd64-perf builder seems to be passing consistently for
  x/benchmarks and x/tools, so there is no need to refer to
  golang/go#53538 to explain failures on it.

Change-Id: Ia16db2a23e5fa037a299f1f56fb26f1cf84521e1
Reviewed-on: https://go-review.googlesource.com/c/build/+/465156
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

dashboard/builders.go

@@ -2612,7 +2612,6 @@ func init() {
 			"GOHOSTOS=linux",
 			"CGO_ENABLED=1",
 		},
-		KnownIssues: []int{42212, 51001, 52724},
 	})
 	addBuilder(BuildConfig{
 		Name:              "android-amd64-emu",
@@ -2644,18 +2643,16 @@ func init() {
 			"GOHOSTOS=linux",
 			"CGO_ENABLED=1",
 		},
-		KnownIssues: []int{42212, 51001, 52724},
 	})
 	addBuilder(BuildConfig{
 		Name:     "illumos-amd64",
 		HostType: "host-illumos-amd64-jclulow",
 	})
 	addBuilder(BuildConfig{
-		Name:        "solaris-amd64-oraclerel",
-		HostType:    "host-solaris-oracle-amd64-oraclerel",
-		Notes:       "Oracle Solaris release version",
-		FlakyNet:    true,
-		KnownIssues: []int{51443},
+		Name:     "solaris-amd64-oraclerel",
+		HostType: "host-solaris-oracle-amd64-oraclerel",
+		Notes:    "Oracle Solaris release version",
+		FlakyNet: true,
 	})
 	addBuilder(BuildConfig{
 		Name:           "linux-ppc64-sid-buildlet",
@@ -2768,7 +2765,6 @@ func init() {
 			"GOARCH=loong64",
 			"GOHOSTARCH=loong64",
 		},
-		KnownIssues: []int{53116, 53093},
 	})
 	addBuilder(BuildConfig{
 		FlakyNet:       true,
@@ -3023,7 +3019,6 @@ func init() {
 		},
 		RunBench:     true,
 		SkipSnapshot: true,
-		KnownIssues:  []int{53538},
 	})
 }