[LyX/master] Remove unused member.

[Jean-Marc Lasgouttes]

commit db1979f398716185116a93a7c46fac4efe20340b
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Thu Mar 5 12:30:12 2015 +0100

    Remove unused member.
    
    Fixes coverity issue 23413.

diff --git a/src/LyX.cpp b/src/LyX.cpp
index a96531f..251fe2d 100644
--- a/src/LyX.cpp
+++ b/src/LyX.cpp
@@ -176,7 +176,7 @@ struct LyX::Impl {
        Movers system_movers_;
 
        /// has this user started lyx for the first time?
-       bool first_start;
+//     bool first_start;
        /// the parsed command line batch command if any
        vector<string> batch_commands;