[lldb] Devirtualize IOHandler::{IsActive,SetIsDone,GetIsDone} (NFC)

There are no implementations overriding these methods.

Differential revision: https://reviews.llvm.org/D120766

(cherry picked from commit 37eb15a)

Author: JDevlieghere

lldb/include/lldb/Core/IOHandler.h

@@ -85,11 +85,11 @@ class IOHandler {
 
   virtual void GotEOF() = 0;
 
-  virtual bool IsActive() { return m_active && !m_done; }
+  bool IsActive() { return m_active && !m_done; }
 
-  virtual void SetIsDone(bool b) { m_done = b; }
+  void SetIsDone(bool b) { m_done = b; }
 
-  virtual bool GetIsDone() { return m_done; }
+  bool GetIsDone() { return m_done; }
 
   Type GetType() const { return m_type; }