Revert "Forward code coverage flags."

[maleadt]

Reverts #94

Looking at the flag forwarding behavior of julia_cmd() as part of #96, it turns out the non-forwarding design is very much intended:

❯ julia --code-coverage=user -e 'println(Base.julia_cmd())'
`julia -C native -g1 --code-coverage=user`

~
❯ julia --code-coverage="lcov-%p.info" -e 'println(Base.julia_cmd())'
`julia -C native -g1 --code-coverage=all --code-coverage=/Users/tim/lcov-%p.info`

~
❯ julia --code-coverage="lcov.info" -e 'println(Base.julia_cmd())'
`julia -C native -g1`

i.e. there is an if isempty(coverage_file) || occursin("%p", coverage_file) check to avoid clobbering the same output file.