Revert "Upgrade wayland.xml to version 1.10.0"

Since we're using the deprecated ways of including wayland (wayland-server.h
instead of wayland-server-core.h), we can't upgrade wayland.xml to a version
that's newer than the system libwayland. Our minimum supported version is 1.6.

This reverts commit 1d51503daead2e09cc2526a0114bedd4669c1d3f.

Fixes: QTBUG-70528
Change-Id: I102cb215a40a1aaaeba6f463200eefc3be653c52
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/3rdparty/wayland/protocols/qt_attribution.json

@@ -8,8 +8,8 @@
 
         "Description": "Wayland is a protocol for a compositor to talk to its clients.",
         "Homepage": "https://wayland.freedesktop.org",
-        "Version": "1.10.0",
-        "DownloadLocation": "https://cgit.freedesktop.org/wayland/wayland/tag/?id=1.10.0",
+        "Version": "1.6.1",
+        "DownloadLocation": "https://cgit.freedesktop.org/wayland/wayland/tag/?id=1.6.1",
         "LicenseId": "HPND",
         "License": "HPND License",
         "LicenseFile": "HPND_LICENSE.txt",