Swift: remove double newlines in schema

While PEP8 mandates those, they look bad in the schema file.

`autopep8` already ignores those, and they were single newlines at some
point until an overeager IDE has "fixed" them at some point without me
realizing.

Also, the pre-commit configuration was updated to take `schema.py` into
account.

.pre-commit-config.yaml

@@ -19,7 +19,7 @@ repos:
     rev: v1.6.0
     hooks:
       - id: autopep8
-        files: ^swift/codegen/.*\.py
+        files: ^swift/.*\.py
 
   - repo: local
     hooks:
@@ -44,7 +44,7 @@ repos:
 
       - id: swift-codegen
         name: Run Swift checked in code generation
-        files: ^swift/(codegen/|.*/generated/|ql/lib/(swift\.dbscheme$|codeql/swift/elements))
+        files: ^swift/(schema.py$|codegen/|.*/generated/|ql/lib/(swift\.dbscheme$|codeql/swift/elements))
         language: system
         entry: bazel run //swift/codegen -- --quiet
         pass_filenames: false