ARROW-3423: [Packaging] Remove RC information from deb/rpm packages

[kou]

Because we reuse RC packages as the official release packages when our
vote is passed.

[kszucs]

I'm not sure I fully understand, but the latest binaries didn't contain the rc postfix https://www.apache.org/dist/arrow/arrow-0.10.0/binaries/ubuntu-bionic/

[wesm]

I don't understand why this wasn't an issue with the last release, but feel free to merge if this unblocks the release

[kou]

the latest binaries didn't contain the rc postfix

Because we don't care RC information at all at 0.10.0 release:
https://github.com/apache/arrow/blob/apache-arrow-0.10.0/dev/tasks/linux-packages/Rakefile#L44-L52

We don't use the source archive at dist.apache.org at 0.10.0 release but we start using the source archive at dist.apahce.org since 0.11.0: #2441

Normally, including RC information is better in deb/rpm packages. Because users that install RC packages can upgrade to the official release smoothly. I want to reuse dev/tasks/linux-packages/package-task.rb in other projects. So I want to keep the current RC support feature and treat Apache Arrow case as a special case.

This is needed to release deb/rpm packages for 0.11.0 with the source archive at dist.apache.org. So I'll merged this.