THRIFT-2275 Fix memory leak in golang compact_protocol.

Patch: bolin huang
diff --git a/lib/go/thrift/compact_protocol.go b/lib/go/thrift/compact_protocol.go
index 74d36d0..f89fc2f 100644
--- a/lib/go/thrift/compact_protocol.go
+++ b/lib/go/thrift/compact_protocol.go
@@ -352,6 +352,7 @@
 func (p *TCompactProtocol) ReadStructEnd() error {
 	// consume the last field we read off the wire.
 	p.lastFieldId = p.lastField[len(p.lastField)-1]
+	p.lastField = p.lastField[:len(p.lastField)-1]
 	return nil
 }