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#>