treewide: Remove indefinite article from meta.description

nix run nixpkgs#silver-searcher -- -G '\.nix$' -0l 'description.*"[Aa]n?' pkgs \
  | xargs -0 nix run nixpkgs#gnused -- -i '' -Ee 's/(description.*")[Aa]n? (.)/\1\U\2/'

pkgs/development/python-modules/astroid/default.nix

@@ -39,7 +39,7 @@ buildPythonPackage rec {
 
   meta = with lib; {
     changelog = "https://github.com/PyCQA/astroid/blob/${src.rev}/ChangeLog";
-    description = "An abstract syntax tree for Python with inference support";
+    description = "Abstract syntax tree for Python with inference support";
     homepage = "https://github.com/PyCQA/astroid";
     license = licenses.lgpl21Plus;
     maintainers = with maintainers; [ GaetanLepage ];