Pull Emacs 27 from @tazjin's depot

Here's what happened:

My `emacs.glinux` derivation relies on gLinux `/usr/bin/emacs`, and Google
recently published version 27, so all corporate machines (i.e. this laptop)
switched from Emacs 26 to Emacs 27 overnight.

However, my Nix derivation was building all of the packages for Emacs 26, so
some packages were compatible while others weren't.

The Elisp package, `emr`, doesn't build for version 27, so I dropped it
altogether.

1 files changed, 1 insertions, 1 deletions

diff --git a/default.nix b/default.nix
index dca6dea16c23..bb8c557cdc81 100644
--- a/default.nix
+++ b/default.nix
@@ -12,7 +12,7 @@ let
 
   depot = import (fetchGit {
     url = "https://cl.tvl.fyi/depot";
-    rev = "a2e86152401c7c531801c79347c3f15e1806aabc";
+    rev = "2f7b688389058b454ee12adc4b6b47740298f53b";
   }) {};
 
   pkgs = import (fetchGit {