[LyX/2.1.x] Revert "Now math previews are correctly updated when replacing math contents inside"

[Scott Kostyshak]

commit 400db01c2a6fcce5d24c6848e89fb65b64a07a57
Author: Scott Kostyshak <skost...@lyx.org>
Date:   Fri Nov 13 20:06:45 2015 -0500

    Revert "Now math previews are correctly updated when replacing math 
contents inside"
    
    This commit reverts 73ad885a and 29948eec.
    
    Updating all previews is expensive. See #7242 for details.

diff --git a/src/lyxfind.cpp b/src/lyxfind.cpp
index 51e0db3..78d8f28 100644
--- a/src/lyxfind.cpp
+++ b/src/lyxfind.cpp
@@ -1426,7 +1426,6 @@ static void findAdvReplace(BufferView * bv, 
FindAndReplaceOptions const & opt, M
        LYXERR(Debug::FIND, "After pos adj cur=" << cur << " with depth: " << 
cur.depth() << " and len: " << sel_len);
        bv->putSelectionAt(DocIterator(cur), sel_len, !opt.forward);
        bv->processUpdateFlags(Update::Force);
-       bv->buffer().updatePreviews();
 }