docs(setup): remove mention of STC project because stc is offically abandoned

[ryoppippi]

dudykr/stc#1101

Before submitting a Pull Request, please test your code.

If you created a new feature, then create the unit test function, too.

# COMPILE
npm run build

# RE-WRITE TEST PROGRAMS IF REQUIRED
npm run test:template

# BUILD TEST PROGRAM
npm run build:test

# DO TEST
npm run test

Learn more about the CONTRIBUTING

[samchon]

I am preparing new setup docs for unpluggin and did the same thing.

However, this PR is still good because the new setup docs need much more times.