Remove last used speech engine from feature server updating query in mysql

[vdharashive]

it is not required to store the last update speech engine in mysql database , since there will be lot of db update in mysql which is performance concern

Mysql can be used only for read only form all the jambonz services other then webapps and API server

Last used speech engine setting can be maintained in Redis

[rammohan-y]

As per discussion with @davehorton we will be removing the last_used from UI and stop calling updateSpeechCredentialLastUsed method in feature-server module

[davehorton]

along with this we will need to update the webapp to not show it as well

[rammohan-y]

PR for webapp: jambonz/jambonz-webapp#460
PR for feature-server: #944

Please see below picture after removal of last used column.