[CI] Remove now unnecessary Dockerfile for centos-7

[raulcd]

Describe the enhancement requested

When dropping centos-7 packages we left the

arrow/ci/docker/centos-7-cpp.dockerfile

Line 4 in 016e3cf

# regarding copyright ownership. The ASF licenses this file

and it's related docker-compose service because it was used on the R OpenSSL 1.x jobs.

A little bit after #40735 was merged #45449 was also merged but the docker file hasn't been removed.

This is to remove the now unnecessary Dockerfile.

Component(s)

Continuous Integration

[kou]

Issue resolved by pull request 48573
#48573