Revert "Revert "[clang-format] Keep protobuf "package" statement on one line""

Summary:
Top-level "package" and "import" statements should generally be kept on
one line, for all languages.

----

This reverts commit rL356912.
The regression from rL356835 was fixed via rC358275.

Reviewers: krasimir, sammccall, MyDeveloperDay, xinz, dchai, klimek

Reviewed By: krasimir, xinz, dchai

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60661

llvm-svn: 360411