Move wlr_gamma_control_manager_v1 to patch

[djpohly]

Gamma control is a protocol that not everyone uses/needs, but it was added to dwl core because the SLOC impact was negligible. Since this is no longer the case with wlroots 0.17 (it now costs us 24 lines), I propose moving the wlr_gamma_control_manager_v1 implementation into a patch for wlroots-next.