unused variable ison_count_histogram_buffer in db_maint.cpp

Following warning is shown while peerplays develop branch testnet code is built

/home/kiran/PBSA/peerplays/peerplays/witness/peerplays/libraries/chain/db_maint.cpp:723:21: warning: unused variable ‘son_count_histogram_buffer’ [-Wunused-variable]

kiran@warpspeed:~/PBSA/peerplays/peerplays/witness/peerplays$ git log -2
commit 0856e898bb2d0fbe60f9261332049088881bc01f (HEAD -> develop, origin/develop)
Merge: 1b1df250 4db9f3a1
Author: serkixenos <serki.xenos@gmail.com>
Date:   Mon Oct 3 17:34:01 2022 +0000

    Merge branch 'update-cli-wallet-docs' into 'develop'
    
    Update cli wallet docs
    
    See merge request PBSA/peerplays!162

commit 4db9f3a15bfb25ac823a73b50d23dd2e381d87e0
Author: serkixenos <serki.xenos@gmail.com>
Date:   Mon Oct 3 17:34:01 2022 +0000

    Update cli wallet docs
kiran@warpspeed:~/PBSA/peerplays/peerplays/witness/peerplays$

full logs attached. peerplays-witness-develp-10102022.log