Switch to upstream version of FindWaylandProtocols

FindWaylandProtocols has been upstreamed to ECM.

src/wayland/cmake/Modules/FindWaylandProtocols.cmake

-#.rst:
-# FindWaylandProtocols
-# -------
-#
-# Try to find wayland-protocols on a Unix system.
-#
-# This will define the following variables:
-#
-# ``WaylandProtocols_FOUND``
-#     True if (the requested version of) wayland-protocols is available
-# ``WaylandProtocols_VERSION``
-#     The version of wayland-protocols
-# ``WaylandProtocols_DATADIR``
-#     The wayland protocols data directory
-
-#=============================================================================
-# SPDX-FileCopyrightText: 2019 Vlad Zahorodnii <vlad.zahorodnii@kde.org>
-#
-# SPDX-License-Identifier: BSD-3-Clause
-#=============================================================================
-
-find_package(PkgConfig)
-pkg_check_modules(PKG_wayland_protocols QUIET wayland-protocols)
-
-set(WaylandProtocols_VERSION ${PKG_wayland_protocols_VERSION})
-pkg_get_variable(WaylandProtocols_DATADIR wayland-protocols pkgdatadir)
-
-include(FindPackageHandleStandardArgs)
-find_package_handle_standard_args(WaylandProtocols
-    FOUND_VAR WaylandProtocols_FOUND
-    REQUIRED_VARS WaylandProtocols_DATADIR
-    VERSION_VAR WaylandProtocols_VERSION
-)
-
-include(FeatureSummary)
-set_package_properties(WaylandProtocols PROPERTIES
-    DESCRIPTION "Specifications of extended Wayland protocols"
-    URL "https://wayland.freedesktop.org/"
-)