std.log: don't state in docs that messages are logged to stderr
std.log: don't state in docs that messages are logged to stderr

Since the logger implementation can be overridden, the messages might
not be logged to stderr at all.

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