vendor: botan: simplify foreign import

vendor/botan/bindings/botan.odin

@@ -142,11 +142,7 @@ fpe_t                :: ^fpe_struct
 
 when ODIN_OS == .Windows {
     foreign import botan_lib "botan.lib"
-} else when ODIN_OS == .Linux {
-    foreign import botan_lib "system:botan-2"
-} else when ODIN_OS == .Darwin {
-    foreign import botan_lib "system:botan-2"
-} else when ODIN_OS == .OpenBSD {
+} else {
     foreign import botan_lib "system:botan-2"
 }