internal/migration: stop running more builders

We've considered porting these builders but decided not to at this time.
We have a standard Debian builder in many run-mod variations, and a Sid
builder which aims to use a newer Linux kernel version. If we encounter
compelling motivation to have more per-distro builders, we will revisit
this. Stop the legacy builders now.

Also mark windows-arm-zx2c4 as something that's not going to be ported,
as the windows/arm port is slated for removal.

For golang/go#60468.
For golang/go#67761.

Change-Id: I595ff2df382130f6eaeca8f1a163f4939fc4873e
Reviewed-on: https://go-review.googlesource.com/c/build/+/672216
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
diff --git a/internal/migration/migration.go b/internal/migration/migration.go
index bea9f56..24e0da8 100644
--- a/internal/migration/migration.go
+++ b/internal/migration/migration.go
@@ -37,13 +37,17 @@
 
 	// Linux builders (just those covering first-class ports).
 	"linux-386": true, "linux-386-bullseye": true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-386.
+	"linux-386-buster":    true,                               // Intentionally chosen not to keep running in LUCI at this time. Deemed as ported so it can be stopped.
 	"linux-386-longtest":  true,                               // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-386-longtest.
 	"linux-386-clang":     true,                               // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-386-clang15 (a newer clang, but we won't be adding exactly -clang7 to LUCI by now).
 	"linux-386-sid":       true,                               // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-386_debiansid.
 	"linux-386-softfloat": true,                               // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-386-softfloat.
 	"linux-arm-aws":       true,                               // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-arm.
 	"linux-amd64":         true, "linux-amd64-bullseye": true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-amd64.
+	"linux-amd64-alpine":            true, // Intentionally chosen not to keep running in LUCI at this time. Deemed as ported so it can be stopped.
+	"linux-amd64-buster":            true, // Intentionally chosen not to keep running in LUCI at this time. Deemed as ported so it can be stopped.
 	"linux-amd64-bookworm":          true, // Available (in a GOARCH=arm64 variant) as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-arm64.
+	"linux-amd64-fedora":            true, // Intentionally chosen not to keep running in LUCI at this time. Deemed as ported so it can be stopped.
 	"linux-amd64-longtest":          true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-amd64-longtest.
 	"linux-amd64-perf":              true, // Available in the form of multiple linux-amd64_…-perf_vs_… LUCI builders.
 	"linux-amd64-race":              true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-amd64-race.
@@ -68,6 +72,7 @@
 	"windows-amd64-2016":     true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-windows-amd64.
 	"windows-amd64-longtest": true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-windows-amd64-longtest.
 	"windows-amd64-race":     true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-windows-amd64-race.
+	"windows-arm-zx2c4":      true, // Intentionally chosen not to keep running in LUCI at this time. Deemed as ported so it can be stopped.
 	"windows-arm64-11":       true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-windows-arm64.
 
 	"linux-riscv64-jsing":      true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-riscv64.