WASM: Enable exception handling tests

compiler/testData/codegen/box/exclExcl/genericNull.kt

@@ -1,5 +1,4 @@
-// DONT_TARGET_EXACT_BACKEND: WASM
-// WASM_MUTE_REASON: EXCEPTIONS_NOT_IMPLEMENTED
+
 fun <T> foo(t: T) {
     t!!
 }

compiler/testData/codegen/box/exclExcl/kt48440.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: WASM
-
 fun test(): String {
     var exception: Throwable? = null
     val f = {

compiler/testData/codegen/box/exclExcl/kt48440_2.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: WASM
-
 fun <T> id(t: T): T = t
 
 fun test(b: Boolean): String {