tree-sitter-grammars: remove agda as it is abandoned

pkgs/development/tools/parsing/tree-sitter/grammars/default.nix

···
 { lib }:
 {
-  tree-sitter-agda = lib.importJSON ./tree-sitter-agda.json;
   tree-sitter-bash = lib.importJSON ./tree-sitter-bash.json;
   tree-sitter-beancount = lib.importJSON ./tree-sitter-beancount.json;
   tree-sitter-bibtex = lib.importJSON ./tree-sitter-bibtex.json;

pkgs/development/tools/parsing/tree-sitter/grammars/tree-sitter-agda.json

···
-{
-  "url": "https://github.com/tree-sitter/tree-sitter-agda",
-  "rev": "d710ff14d15ddee3764fd73a0837c6c4c8c913e9",
-  "date": "2019-09-20T18:06:06+08:00",
-  "path": "/nix/store/wqz9v9znaiwhhqi19hgig9bn0yvl4i9s-tree-sitter-agda",
-  "sha256": "1wpfj47l97pxk3i9rzdylqipy849r482fnj3lmx8byhalv7z1vm6",
-  "fetchLFS": false,
-  "fetchSubmodules": false,
-  "deepClone": false,
-  "leaveDotGit": false
-}

pkgs/development/tools/parsing/tree-sitter/update.nix

···
     "tree-sitter-scala"
     "tree-sitter-ocaml"
     "tree-sitter-julia"
-    "tree-sitter-agda"
     "tree-sitter-fluent"
     "tree-sitter-html"
     "tree-sitter-haskell"
···
     "tree-sitter-graph"
     # abandoned
     "tree-sitter-swift"
+    # abandoned
+    "tree-sitter-agda"
   ];
   ignoredTreeSitterOrgReposJson = jsonFile "ignored-tree-sitter-org-repos" ignoredTreeSitterOrgRepos;