Rename libbreezecommon to libbreezecommon5 and don't install .so links

Summary:
libbreezecommon is not meant to be used outside of breeze (it can't, no headers
are installed) so the .so link is not necessary.

Additionally, rename libbreezecommon.so.5 to libbreezecommon5.so.5 for symmetry
with libbreezecommon4.so.5.

Test Plan: Built and installed it - still works.

Reviewers: #breeze, zzag

Reviewed By: zzag

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D14599