[LyX/master] Remove variable that is not used

[Jean-Marc Lasgouttes]

commit d99502d9154e7e51a665f03963e010411e9545be
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Fri Oct 15 15:49:40 2021 +0200

    Remove variable that is not used
    
    Spotted by clang++ 13.
---
 src/frontends/qt/GuiDocument.cpp |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/src/frontends/qt/GuiDocument.cpp b/src/frontends/qt/GuiDocument.cpp
index 9389272..42795bb 100644
--- a/src/frontends/qt/GuiDocument.cpp
+++ b/src/frontends/qt/GuiDocument.cpp
@@ -3109,10 +3109,7 @@ void GuiDocument::updateEngineType(string const & items, CiteEngineType const &
 {
 	engine_types_.clear();
 
-	int nn = 0;
-
 	for (int n = 0; !token(items, '|', n).empty(); ++n) {
-		nn += 1;
 		string style = token(items, '|', n);
 		engine_types_.push_back(style);
 	}