settings: remove _get_{boolean|int|float|string}() APIs

They is really no needed with the new _get() API and the WpSpaJson API. In C,
users can use 'wp_spa_json_parse_{boolean|int|float|string}()' APIs to parse the
WpSpaJson. In Lua, users can just do 'Settings.get(setting, m):parse()'.

src/scripts/policy-endpoint-device.lua

@@ -5,8 +5,8 @@
 --
 -- SPDX-License-Identifier: MIT
 
-local move = Settings.get_boolean ("default-policy-move") or false
-local follow = Settings.get_boolean ("default-policy-follow") or false
+local move = Settings.get ("default-policy-move"):parse() or false
+local follow = Settings.get ("default-policy-follow"):parse() or false
 
 local self = {}
 self.scanning = false