[dvsim] Make email.html filename more descriptive
[dvsim] Make email.html filename more descriptive

This commit makes 2 changes to the generated reports:
- Remove `latest` symlink in the reports area
- Make email.html filename more descriptive, i.e. reflective of
  what hjson cfg was run, the tool flow and the tool.

Signed-off-by: Srikrishna Iyer <2803d640feace36379942447842f26c7747b4dc3@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan