Remove expiration class method and convert platform to class property

OpenVPN Adapter/OpenVPNAdapter+Public.h

@@ -98,6 +98,11 @@ NS_SWIFT_NAME(handle(logMessage:));
  */
 @interface OpenVPNAdapter (Public)
 
+/**
+ Returns platform description
+ */
+@property (class, nonnull, readonly, nonatomic) NSString *platform;
+
 /**
  <#Description#>
  */
@@ -124,16 +129,6 @@ NS_SWIFT_NAME(handle(logMessage:));
  */
 @property (nonnull, readonly, nonatomic) OpenVPNInterfaceStats *interfaceStats;
 
-/**
- Returns date/time of app expiration
- */
-+ (nonnull NSDate *)expiration;
-
-/**
- Returns platform description
- */
-+ (nonnull NSString *)platform;
-
 /**
  <#Description#>
 

OpenVPN Adapter/OpenVPNAdapter.mm

@@ -128,6 +128,11 @@ NSString * const OpenVPNAdapterErrorEventKey = @"me.ss-abramchuk.openvpn-adapter
 
 #pragma mark Properties
 
++ (NSString *)platform {
+    std::string platform = OpenVPNClient::platform();
+    return [NSString stringWithUTF8String:platform.c_str()];
+}
+
 - (void)setDelegate:(id<OpenVPNAdapterDelegate>)delegate {
     _delegate = delegate;
 }
@@ -158,16 +163,6 @@ NSString * const OpenVPNAdapterErrorEventKey = @"me.ss-abramchuk.openvpn-adapter
     return [[OpenVPNInterfaceStats alloc] initWithInterfaceStats:stats];
 }
 
-+ (NSDate *)expiration {
-    NSNumber *time = [NSNumber numberWithInteger:OpenVPNClient::app_expire()];
-    return [NSDate dateWithTimeIntervalSince1970:[time doubleValue]];
-}
-
-+ (NSString *)platform {
-    std::string platform = OpenVPNClient::platform();
-    return [NSString stringWithUTF8String:platform.c_str()];
-}
-
 #pragma mark Client Configuration
 
 - (OpenVPNProperties *)applyConfiguration:(nonnull OpenVPNConfiguration *)configuration error:(out NSError * __nullable * __nullable)error {