Remove partial update functionality

Get rid of the ability of encoders to only send part of the
rectangle they are given as we don't want partial updates
anyway.
diff --git a/common/rfb/HextileEncoder.cxx b/common/rfb/HextileEncoder.cxx
index 0907bab..19fb1a3 100644
--- a/common/rfb/HextileEncoder.cxx
+++ b/common/rfb/HextileEncoder.cxx
@@ -53,8 +53,7 @@
 {
 }
 
-bool HextileEncoder::writeRect(const Rect& r, TransImageGetter* ig,
-                               Rect* actual)
+void HextileEncoder::writeRect(const Rect& r, TransImageGetter* ig)
 {
   writer->startRect(r, encodingHextile);
   rdr::OutStream* os = writer->getOutStream();
@@ -82,5 +81,4 @@
     break;
   }
   writer->endRect();
-  return true;
 }