FIR: Unignore all Fir2IrText tests on context receivers

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

@@ -1,5 +1,4 @@
 // !LANGUAGE: +ContextReceivers
-// IGNORE_BACKEND_FIR: JVM_IR
 
 class C {
     val c = 42
@@ -14,4 +13,4 @@ fun bar(c: C) {
     with(c) {
         foo()
     }
-}
+}