Undo addition of "(AI)" F-15E variant.

This interacts badly with the built-in squadrons:
https://github.com/dcs-liberation/dcs_liberation/issues/3033. Better to
split the display name and "ID" (which is effectively how the key here
is treated), but that's a more invasive change than I'd like to tackle
in this release.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/3033.

resources/units/aircraft/F-15E.yaml

@@ -11,7 +11,6 @@ role: Multirole Strike Fighter
 max_range: 300
 variants:
   F-15E Strike Eagle: {}
-  F-15E Strike Eagle (AI): {}
 tasks:
   BAI: 760
   BARCAP: 240