Remove unused private field freeDiskSpaceKB

Static analysis identified an unused private
field freeDiskSpaceKB in the EncoderLink class.
The usage was remove in commit a4796b5
'Storage Groups (a novel by Chris Pinkham)',
but the variable remained.  Remove it from
the class and ctors

mythtv/programs/mythbackend/encoderlink.cpp

@@ -40,7 +40,7 @@ using namespace std;
 EncoderLink::EncoderLink(int capturecardnum, PlaybackSock *lsock,
                          QString lhostname)
     : m_capturecardnum(capturecardnum), sock(lsock), hostname(lhostname),
-      freeDiskSpaceKB(-1), tv(NULL), local(false), locked(false),
+      tv(NULL), local(false), locked(false),
       sleepStatus(sStatus_Undefined), chanid(0)
 {
     endRecordingTime = MythDate::current().addDays(-2);
@@ -59,7 +59,7 @@ EncoderLink::EncoderLink(int capturecardnum, PlaybackSock *lsock,
  */
 EncoderLink::EncoderLink(int capturecardnum, TVRec *ltv)
     : m_capturecardnum(capturecardnum), sock(NULL),
-      freeDiskSpaceKB(-1), tv(ltv), local(true), locked(false),
+      tv(ltv), local(true), locked(false),
       sleepStatus(sStatus_Undefined), chanid(0)
 {
     endRecordingTime = MythDate::current().addDays(-2);

mythtv/programs/mythbackend/encoderlink.h

@@ -142,8 +142,6 @@ class EncoderLink
     PlaybackSock *sock;
     QString hostname;
 
-    long long freeDiskSpaceKB;
-
     TVRec *tv;
 
     bool local;