wtstats template source files not required in mongo repo

WiredTiger's tools directory has been reorganized and the wtstats tool now lives in a separate sub-directory ./tools/wtstats/

This needs to be reflected in the update-vendor-wiredtiger script.

Currently, the script no longer excludes the ./template source dir and commits the entire dir to the mongo repo, which is not necessary. All that is required is wtstats.py, stat_data.py and wtstats.html.template, both located in ./tools/wtstats/.

https://github.com/mongodb/mongo/blob/master/buildscripts/update-vendor-wiredtiger#L45

This line should instead exclude */tools/wtstats/template instead.