FIR: Unignore all blackbox tests on context receivers

compiler/testData/codegen/box/extensionFunctions/contextReceivers/propertyCompoundAssignment.kt

@@ -1,7 +1,5 @@
 // !LANGUAGE: +ContextReceivers
 // TARGET_BACKEND: JVM_IR
-// IGNORE_BACKEND_FIR: JVM_IR
-// FIR status: context receivers aren't yet supported
 
 class LoggingCounter {
     var operationCounter = 0
@@ -31,4 +29,4 @@ fun box(): String {
     }
     val operationsTotal = loggingCounter.operationCounter
     return if (operationsTotal == 5) "OK" else "$operationsTotal"
-}
+}