Use straight for agda

We can fetch the mode directly from straight. There's no need to rely on
having this .el file installed for us. Now agda's el files can be edited
directly like all other emacs packages.

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

modules/lang/agda/packages.el

@@ -0,0 +1,15 @@
+;; -*- no-byte-compile: t; -*-
+;;; lang/agda/packages.el
+
+
+(package! agda-input
+  :recipe
+  (:host github :repo "agda/agda"
+         :files ("src/data/emacs-mode/agda-input.el")))
+
+(package! agda2-mode
+  :recipe
+  (:host github :repo "agda/agda"
+         :files
+         ("src/data/emacs-mode/*.el"
+          (:exclude "agda-input.el"))))