modules/input: don't dist generated protocol sources

For some reason modules/input adds the C code that is generated by
wayland-scanner to EXTRA_DIST. This results in a race where depending
on the timestamps of the tarball and the timestamp of the system
wayland-protocols either the generated source in the tarball or a
regenerated source will be used.

This doesn't actually impact the code generated, but it does break
reproducible builds as the list of source files changes.
8 jobs for protocol in 35 minutes and 13 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #792730
debian-meson

00:07:12

passed #792727
fedora-autotools

00:20:53

manual #792728
allowed to fail manual
fedora-distcheck
passed #792729
fedora-meson

00:09:35

manual #792732
win32-ps allowed to fail manual
msys2-mingw64-autotools
passed #792792
win32-ps
msys2-mingw64-meson

00:02:17

failed #792731
win32-ps
msys2-mingw64-meson

00:04:09

 
  Docs
passed #792733
reference

00:12:02