Make latch_map_file truly optional

[edwardcwang]

Right now if a technology doesn't specify the latch map file, "techmap -map None" is written into the generated tcl.

Type of change: Bugfix

Impact: Change to a Hammer plugin

Contributor Checklist:

• Did you set master as the base branch?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you update the poetry.lock file if you updated the requirements in pyproject.toml?
• (If applicable) Did you add a unit test demonstrating the PR?
• (If applicable) Did you run this through the e2e integration tests?
• (If applicable) Did you update the submodules in e2e/ if this feature depends on updated plugins?