[roll] Roll fuchsia [wlan] Relocate and simplify wifi network helpers from base test to specific tests

Relocate `get_psk_network()`, `get_open_network()`, and `get_wep_network()`
out of the shared deprecated `WifiBaseTest` base class in preparation
to migrate tests from the Antlion base test class to the Lacewing base test
class:
- Deleted all three unused helper methods from `base_test.py`.
- Added a highly simplified, parameter-free version of `get_psk_network()`
  and `get_open_network()` directly to `PolicyScanTest.py` at its original
  location, utilizing local SSID/passphrase length constants and
  `AccessPointConfig.random_string()`.
- Added a simplified version of `get_open_network()` (supporting local min/max
  SSID length constants) to `WlanPhyComplianceABGTest.py` to avoid breakage
  in compliance tests.
- Discarded all unused dictionary keys (like "hiddenSSID", "wepKeys", "ieee80211w")
  from the returned dictionaries to clean up dependencies.

This cleans up the legacy base class and isolates testbed setup parameters
specifically to the tests that need them, removing deprecated helpers.

Original-Original-Bug: 500737382
Test: http://cr-buildbucket.appspot.com/build/8681253448414203889
Test: http://cr-buildbucket.appspot.com/build/8681226607587236449
Test: http://cr-buildbucket.appspot.com/build/8681225763586699057
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1618034
Original-Original-Revision: f6d9763e7a931367af66541ff49d965108381aca
GitOrigin-RevId: a8288e46e08b9fee8b85c60202068977a7040118
Change-Id: I2450caf273971fadb708f605dd0844d1b7ca7eb3
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1621496
Cr-Commit-Position: refs/heads/main@{#193331}