Remove confusing GetFirstPad() call

This no longer returns the first pad, just the first by pad sort order
in output.  The call is not used correctly in pcbnew, so removing to
prevent future misuse

pcbnew/footprint.cpp

@@ -913,7 +913,7 @@ PAD* FOOTPRINT::GetPad( const wxPoint& aPosition, LSET aLayerMask )
 
 PAD* FOOTPRINT::GetTopLeftPad()
 {
-    PAD* topLeftPad = GetFirstPad();
+    PAD* topLeftPad = m_pads.front();
 
     for( PAD* p : m_pads )
     {

pcbnew/footprint.h

@@ -507,16 +507,6 @@ public:
 
     PAD* GetTopLeftPad();
 
-    /**
-     * Get the first pad in the list or NULL if none.
-     *
-     * @return first pad or null pointer.
-     */
-    PAD* GetFirstPad() const
-    {
-        return m_pads.empty() ? nullptr : m_pads.front();
-    }
-
     /**
      * Return the number of pads.
      *