Remove non-const TV play lock functions

The lock functions in tv_play.cpp are now all const.
For two lock functions there was both a const and a non-const variant
with identical function bodies.
It appears that there is no need for the non-const variants; all code
compiles without warnings against the const variants.
Therefore the non-const variants have been removed.

mythtv/libs/libmythtv/tv_play.cpp

@@ -10129,33 +10129,23 @@ OSD *TV::GetOSDL()
     return nullptr;
 }
 
-void TV::ReturnOSDLock()
+void TV::ReturnOSDLock() const
 {
     if (m_player)
         m_player->UnlockOSD();
     m_playerContext.UnlockDeletePlayer(__FILE__, __LINE__);
 }
 
-void TV::GetPlayerWriteLock()
+void TV::GetPlayerWriteLock() const
 {
     m_playerLock.lockForWrite();
 }
 
-void TV::GetPlayerReadLock()
-{
-    m_playerLock.lockForRead();
-}
-
 void TV::GetPlayerReadLock() const
 {
     m_playerLock.lockForRead();
 }
 
-void TV::ReturnPlayerLock()
-{
-    m_playerLock.unlock();
-}
-
 void TV::ReturnPlayerLock() const
 {
     m_playerLock.unlock();

mythtv/libs/libmythtv/tv_play.h

@@ -262,11 +262,9 @@ class MTV_PUBLIC TV : public TVPlaybackState, public MythTVMenuItemDisplayer, pu
 
     // Lock handling
     OSD* GetOSDL();
-    void ReturnOSDLock();
-    void GetPlayerWriteLock();
-    void GetPlayerReadLock();
+    void ReturnOSDLock() const;
+    void GetPlayerWriteLock() const;
     void GetPlayerReadLock() const;
-    void ReturnPlayerLock();
     void ReturnPlayerLock() const;
 
     // Other toggles