FIR: Unignore all Fir2IrText tests on context receivers

compiler/testData/ir/irText/declarations/contextReceivers/class.kt

@@ -1,5 +1,4 @@
 // !LANGUAGE: +ContextReceivers
-// IGNORE_BACKEND_FIR: JVM_IR
 
 class Outer {
     val x: Int = 1
@@ -14,4 +13,4 @@ fun f(outer: Outer) {
     with(outer) {
         Inner(3)
     }
-}
+}