[Regression] SP global destroyScript() no longer exists but is still invoked

Issue

SP provided a destroyScripts() global in the legacy branch, but no longer does in the master branch. The scripts supply_drop.lua and border_defend_station.lua still invoke it in their update loops when the entity they're associated with no longer exists, and its absence causes the scripts to emit an attempt to call a nil value error every update.

Steps to reproduce

Requires applying the workaround in #2593 first.

1. Launch any scenario with station entities, such as scenario_00_basic.lua.
2. Open comms with a station and order a supply drop.
3. Destroy the supply drop ship.

Expected behavior

The supply drop ship is destroyed without error. The supply_drop.lua script no longer runs.

Observed behavior

The supply drop ship is destroyed, but the supply_drop.lua script continues running. Every tick emits an error:

supply_drop.lua:15: attempt to call a nil value (global `destroyScript`)

Inspect supply_drop.lua and border_defend_station.lua, especially their update loops, and compare the current lifecycle behavior with the legacy destroyScripts() handling. Reproduce with the workaround from #2593 in scenario_00_basic.lua by destroying the supply drop ship. Done means the associated script stops running without emitting a nil-value error.