Simplify the property declarations for Spring.
Simplify the property declarations for Spring.

Summary: Swift will infer the type signature. We don't need to provide it ourselves.

Reviewers: chuga, O4 Material Apple platform reviewers, O2 Material Motion, #material_motion

Reviewed By: chuga, O4 Material Apple platform reviewers

Tags: #material_motion

Differential Revision: http://codereview.cc/D2579

material-motion/material-motion-swift,material-motion/material-motion-swift