ci: retire the CircleCI job, GitHub Actions already supersedes it

emulator-build-test duplicated the integration job in .github/workflows,
and did the same work worse in three ways:

  * it cloned firmware `master` unconditionally, so any branch carrying a
    newer test harness ran against older firmware and failed for reasons the
    PR did not cause. That is why it has been red since build #673 while
    GitHub Actions stayed green on the same commits.
  * it set no timeouts, so a hung test produced no output until CircleCI
    killed the job at ten minutes -- reported as a timeout rather than a
    failing test, and discarding every result after the hang.
  * it also ran the firmware's C++ firmware-unit suite, which covers firmware
    code that no change in this repo can affect, and which the firmware repo
    already runs in its own CI.

The integration job builds from current firmware and bounds every step with
timeout-minutes, so a hang fails fast and names the test.

master has no required status checks, so removing the context does not block
any pull request. Also corrects the ci.yml header, which still described
pulling a published DockerHub image -- the job stopped doing that when it
started building from firmware.

Author: BitHighlander

.circleci/config.yml

@@ -1,13 +1,34 @@
 # KeepKey python-keepkey CI
 #
-# Pulls the published emulator image (kktech/kkemu) from DockerHub
-# and runs the full python integration test suite against it.
+# BUILDS an emulator from current firmware and runs the full python
+# integration suite against it. It does not pull a published image: a
+# published image ages out of step with the tests, and a suite that gates on
+# requires_firmware() then SKIPS instead of failing, so the run stays green
+# while covering nothing.
 #
 # Stage 1: GATE (seconds)
 #   └─ lint        basic Python syntax check
 #
 # Stage 2: TEST (gated by Stage 1)
 #   └─ integration full pytest suite against emulator
+#
+# This is the ONLY CI for this repo. A CircleCI job (emulator-build-test) used
+# to run alongside it and was retired -- see .circleci/config.yml in history.
+# It is not worth restoring:
+#
+#   * It cloned firmware `master` unconditionally, so a branch carrying a newer
+#     test harness was always run against older firmware. Tests written for
+#     unreleased firmware then hang or fail for a reason the PR did not cause.
+#   * It set no timeouts. When a test hung, the job produced no output until
+#     CircleCI killed it, reporting a timeout rather than a failing test and
+#     discarding every result after the hang.
+#   * It also ran the firmware's C++ `firmware-unit` suite. That covers firmware
+#     code, which no change in THIS repo can affect, and the firmware repo
+#     already runs it in its own CI.
+#
+# The integration job below fixes the first two directly: it builds from current
+# firmware, and every step is bounded by timeout-minutes so a hang fails fast
+# and points at the test that hung.
 
 name: CI