Update subsurface-libdc to 4.9.3

Summary:
Update subsurface-libdc to 4.9.3

No changelog available.

Packaging change: Switch to github source

Test Plan: Succesfully built and ran Subsurface with this version

Reviewers: Triage Team, DataDrake

Reviewed By: Triage Team, DataDrake

Subscribers: DataDrake

Differential Revision: https://dev.getsol.us/D8458