legacyx86: Drop test on pentium 3

This test nas not been running since at least 2021-03-12 and
nobody seemed to care sufficiently enough.

https://bugzilla.opensuse.org/show_bug.cgi?id=1183454

job_groups/opensuse_tumbleweed_legacy_x86.yaml

@@ -39,8 +39,6 @@ scenarios:
       - create_hdd_textmode
       - gnome
       - install_only
-      - install_only:
-          machine: pentium3
       - kde
       - mediacheck
       - minimalx