subtree(3p/exwm): update & hard reset to commit 'a6e66f5e33'

This contains a bunch of upstream changes after the new maintainers of
EXWM took over, including proper mainlined versions of patches I've
been carrying around here manually.

Notably this undoes the Chromium focus fix patch, lets see how that goes.

git-subtree-dir: third_party/exwm
git-subtree-mainline: a756b46bc70a8a1dbb205d50283a3fe65282ed91
git-subtree-split: a6e66f5e33
Change-Id: Ibcaba379b56611b8f1918c3b60469492d64a3eb7

third_party/overlays/tvl.nix

@@ -49,6 +49,19 @@ depot.nix.readTree.drvTargets {
           self.git
         ];
       });
+
+      # Pin xelb to a newer one until the new maintainers do a release.
+      xelb = eself.trivialBuild {
+        pname = "xelb";
+        version = "0.19-dev"; # invented version, last actual release was 0.18
+
+        src = self.fetchFromGitHub {
+          owner = "emacs-exwm";
+          repo = "xelb";
+          rev = "86089eba2de6c818bfa2fac075cb7ad876262798";
+          sha256 = "1mmlrd2zpcwiv8gh10y7lrpflnbmsycdascrxjr3bfcwa8yx7901";
+        };
+      };
     })
   );