QtMath now provides M_PI constant, operations with degrees, and c++ provides round()

Summary:
Since QtMath library has a proper M_PI the define is not necessary anymore. Furthermore, C++'s round() function behaves in similar fashion to the ROUND2INT macro (rounding away
from zero). If this style of rounding is not specifically required, I suggest another revision to change it to rint(), which rounds towards even numbers.

Reviewers: tcanabrava, rizzitello

Reviewed By: tcanabrava, rizzitello

Subscribers: kde-edu

Tags: #kde_edu

Differential Revision: https://phabricator.kde.org/D16463