Remove parent-relative paths from keyboards.

[tzarc]

Description

Cleanup, relative paths were being defined in a few keyboards, messing with the relative locations in .build/ during build.

In one case, CI was showing issues with intermediate files being removed due to multiple boards from the same manufacturer resulting in the same output file.

For example, rgbkb/sol3 and rgbkb/mun were both targeting:

.build/obj_rgbkb_sol3_rev1/../common/touch_encoder.o   =>   .build/common/touch_encoder.o
.build/obj_rgbkb_mun_rev1/../common/touch_encoder.o    =>   .build/common/touch_encoder.o

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).