emulators/es-de: Unbreak after x11-fonts/ubuntu-font update

The recently updated x11-fonts/ubuntu-font has different names for its
*.ttf files. This broke es-de at runtime, because it explicitly wants to
load "Ubuntu-C.ttf", which isn't provided by ubuntu-font anymore.
The port links to "Ubuntu[wdth,wght].ttf" instead to unbreak es-de.

While here, apply the new framework-provided BUILD_RUN_DEPENDS in place
of the custom _BR_DEPENDS variable.

PR: 298815
Approved by: osa, vvd (Mentors, implicit)