remove single benchmark, it doesn't belong in physics

.gitlab-ci.yml

benchmarks/single/analysis/analyze.cxx

benchmarks/single/analyze.sh

benchmarks/single/common.sh

benchmarks/single/config.yml

benchmarks/single/e-_1GeV_135to177deg.steer

benchmarks/single/e-_1GeV_3to45deg.steer

benchmarks/single/e-_1GeV_45to135deg.steer

benchmarks/single/pi-_1GeV_135to177deg.steer

benchmarks/single/pi-_1GeV_3to45deg.steer

benchmarks/single/pi-_1GeV_45to135deg.steer

benchmarks/single/reconstruct.sh

benchmarks/single/simulate.sh