FIR: Unignore all blackbox tests on context receivers

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

@@ -1,8 +1,5 @@
 // !LANGUAGE: +ContextReceivers
 // TARGET_BACKEND: JVM_IR
-// IGNORE_BACKEND_FIR: JVM_IR
-// FIR status: context receivers aren't yet supported
-
 // KT-51271
 
 class Context {
@@ -36,4 +33,4 @@ fun box(): String = with(Context()) {
         result += 1.testInlineWithExtensionAndMultipleContextsAndArgs()
     }
     return if (result == 23) "OK" else "fail"
-}
+}