Summary:
Don't remove yugabyte-bash-common when performing a clean build.
We were removing the entire build directory when doing a clean-all build, which also
removed yugabyte-bash-common which is already been sourced into the current bash context.
It isn't possible to modify yugabyte-bash-common during a build, it can only be sourced once.
So don't delete it when cleaning the build env.

Test Plan:
jenkins
Ran `yb_build.sh --clean-all` multiple times to ensure everything except yugabyte-bash-common is
deleted.

Reviewers: devops, steve.varnau

Reviewed By: steve.varnau

Subscribers: devops

Differential Revision: https://phorge.dev.yugabyte.com/D40151