[LyX/master] Remove unneeded mutable keywords

[Georg Baum]

commit f3370c3e6a0686b03769e48bcd3fb673925533a9
Author: Georg Baum <b...@lyx.org>
Date:   Tue Nov 18 21:08:43 2014 +0100

    Remove unneeded mutable keywords

diff --git a/src/OutputParams.h b/src/OutputParams.h
index f01c5b9..8663c17 100644
--- a/src/OutputParams.h
+++ b/src/OutputParams.h
@@ -163,11 +163,11 @@ public:
 
        /** Customized bibtex_command
        */
-       mutable std::string bibtex_command;
+       std::string bibtex_command;
 
        /** Customized index_command
        */
-       mutable std::string index_command;
+       std::string index_command;
 
        /** Line length to use with plaintext or LaTeX export.
        */