Revert "Define M_PI if not defined (for MSVC)"

This reverts commit 735411aa47e069105a746a2da1445e9be53eeda0.
Revert "MSVC compile fix (include <limits>, std::size_t). M_PI define fix."

This reverts commit e4c7762ab1950496623286b2c528d408e0556ae2.
Define M_PI when not defined (for MSVC) in IECore/Math.h