[Packaging] Remove RC information from deb/rpm

[asfimport]

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

Reporter: Kouhei Sutou / @kou
Assignee: Kouhei Sutou / @kou

PRs and other links:

• GitHub Pull Request #2694

_{Note: This issue was originally created as ARROW-3423. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 2694
#2694