Drop support for Safari 16 and 17

Safari 16 and 17 runners are no longer reliably available in CI. Saucelabs
still provides them, but session creation failures have been frequent for
weeks now. When this has happened in the past, it's been a prelude to
Saucelabs dropping the affected Safari versions altogether.

We could live with retrying ~30-50% of test runs in the hope that things
might improve, but it's probably better to just rip the band-aid off.

README.md

@@ -30,7 +30,7 @@ Microsoft Edge) as well as Node.
 | Environment       | Supported versions               |
 |-------------------|----------------------------------|
 | Node              | 20, 22, 24                       |
-| Safari            | 16*, 17*, 26*                    |
+| Safari            | 26*                              |
 | Chrome            | Evergreen                        |
 | Firefox           | Evergreen, 102*, 115*, 128*, 140 |
 | Edge              | Evergreen                        |

scripts/run-sauce-browsers

@@ -1,8 +1,8 @@
 #!/bin/sh
 
 # Run tests in supported browsers that are available on Saucelabs.
-# Note: The latest Safari version is tested via GitHub Actions because Saucelabs
-# only makes it available to paid enterprise accounts. See
+# Note: Safari is tested via GitHub Actions because Saucelabs only makes Safari
+# 18 and later available to paid enterprise accounts. See
 # .github/workflows/safari.yml.
 
 run_browser() {
@@ -44,9 +44,6 @@ else
 fi
 run_browser firefox 102
 
-run_browser safari 17
-run_browser safari 16
-
 run_browser MicrosoftEdge latest
 
 echo