std.math: remove constants that should be expressions
std.math: remove constants that should be expressions

All four of these can be represented in fewer characters with
expressions, which will be guaranteed to happen at compile-time, and
have the same or better precision.

The other math constants here which depend on function calls could be
similarly removed if and when #425 is solved. However I left them for
now since Zig does not eagerly evaluate functions with comptime parameters.

raulgrell/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,andrewrk/zig,andrewrk/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig