Remove radius from initdb authentication methods

Hi,

While testing “[a1643d40b] Remove RADIUS support”, I found that initdb still accepts --auth=radius.

See this repro:

1. Run initdb
```
% initdb --auth=radius .
```

2. Check pg_hba.conf, radius is configured there:
```
# "local" is for Unix domain socket connections only
local   all             all                                     radius
# IPv4 local connections:
host    all             all             127.0.0.1/32            radius
# IPv6 local connections:
host    all             all             ::1/128                 radius
```

3. Starting the server fails
```
% pg_ctl -D . start
waiting for server to start....2026-07-01 05:49:51.560 CST [50521] LOG:  starting PostgreSQL 20devel on aarch64-apple-darwin25.5.0, compiled by Apple clang version 21.0.0 (clang-2100.1.1.101), 64-bit
2026-07-01 05:49:51.562 CST [50521] LOG:  listening on IPv6 address "::1", port 5432
2026-07-01 05:49:51.562 CST [50521] LOG:  listening on IPv4 address "127.0.0.1", port 5432
2026-07-01 05:49:51.562 CST [50521] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5432"
2026-07-01 05:49:51.563 CST [50521] LOG:  invalid authentication method "radius"
2026-07-01 05:49:51.563 CST [50521] CONTEXT:  line 113 of configuration file "/Users/chaol/Downloads/pg_data/cndb/pg_hba.conf"
2026-07-01 05:49:51.563 CST [50521] LOG:  invalid authentication method "radius"
2026-07-01 05:49:51.563 CST [50521] CONTEXT:  line 115 of configuration file "/Users/chaol/Downloads/pg_data/cndb/pg_hba.conf"
2026-07-01 05:49:51.563 CST [50521] LOG:  invalid authentication method "radius"
2026-07-01 05:49:51.563 CST [50521] CONTEXT:  line 117 of configuration file "/Users/chaol/Downloads/pg_data/cndb/pg_hba.conf"
2026-07-01 05:49:51.563 CST [50521] LOG:  invalid authentication method "radius"
2026-07-01 05:49:51.563 CST [50521] CONTEXT:  line 120 of configuration file "/Users/chaol/Downloads/pg_data/cndb/pg_hba.conf"
2026-07-01 05:49:51.563 CST [50521] LOG:  invalid authentication method "radius"
2026-07-01 05:49:51.563 CST [50521] CONTEXT:  line 121 of configuration file "/Users/chaol/Downloads/pg_data/cndb/pg_hba.conf"
2026-07-01 05:49:51.563 CST [50521] LOG:  invalid authentication method "radius"
2026-07-01 05:49:51.563 CST [50521] CONTEXT:  line 122 of configuration file "/Users/chaol/Downloads/pg_data/cndb/pg_hba.conf"
2026-07-01 05:49:51.563 CST [50521] FATAL:  could not load /Users/chaol/Downloads/pg_data/cndb/pg_hba.conf
2026-07-01 05:49:51.563 CST [50521] LOG:  database system is shut down
 stopped waiting
pg_ctl: could not start server
Examine the log output.
```

The attached small patch removes radius from initdb's supported auth lists.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/