remove bc from the dependencies

[amtoine]

Should close #70.

As bc is not used anywhere in the code, this PR removes it from the dependencies of bsp-layout.

before the PR

bc is only used in the dependency checks but never as an actual command call

> rg -w bc
install.sh:for dep in bc bspc bash man; do
README.md:* `bc`
src/utils/common.sh:  for dep in bc bspc man; do

after the PR

rg -w bc is empty 👌