wayland-util.h: remove unused math.h include

This header is unused since f5df3895 (2012).
3 jobs for math.h in 1 minute and 35 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Prep
passed #6200937
debian:buster@container-prep

00:00:40

 
  Build
passed #6200938
build-native-autotools

00:00:55

passed #6200939
build-native-meson

00:00:20