WASM: Enable exception handling tests

compiler/testData/codegen/box/arrays/kt503.kt

@@ -1,10 +1,11 @@
-// DONT_TARGET_EXACT_BACKEND: WASM
-// WASM_MUTE_REASON: EXCEPTIONS_NOT_IMPLEMENTED
 // IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND: JS_IR_ES6
 // TODO: muted automatically, investigate should it be ran for JS or not
 // IGNORE_BACKEND: JS
 
+// On Wasm we don't currently have ArrayIndexOutOfBoundsException
+// IGNORE_BACKEND: WASM
+
 fun iarr(vararg a : Int) = a
 fun <T> array(vararg a : T) = a