Prevent jdk_switcher from resetting PATH

Since `/etc/profile.d/load_jdk_switcher.sh` always sources
`$HOME/.jdk_switcher_rc`, jdk_switcher reverting to the original `$PATH`
causes problems when other stuff (such as PostgreSQL service)
starts a login shell after manipulating `$PATH` and subshell is expected
to find stuff in the modified `$PATH`.