Remove .gitattributes and normalize line endings (#29792)

Summary:
The nested `.gitattributes` file in `packages/react-native-codegen/android/` caused some confusion on Linux and macOS, causing Git to show `packages/react-native-codegen/android/gradlew.bat` as modified (CRLF removed, LF added).

Instead of relying on repo-local `.gitattributes` files to convert endings in the working directory, the files should be committed to source control with the correct line endings in the first place. There is no reason to convert LF endings in .sh and many other file to CRLF on Windows (maybe this was an issue a long time ago, but unless Notepad is used this won't be a problem for practically all modern editors).

Also fixed the line endings of `scripts/launchPackager.bat` which was incorrectly committed as LF.

## Changelog

[Internal] [Fixed] - Line endings and .gitattributes

Pull Request resolved: #29792

Test Plan: Clone repo on Linux, macOS, and Windows, and make sure no modified files show up.

Reviewed By: fkgozali

Differential Revision: D23546135

Pulled By: mdvacca

fbshipit-source-id: 1572fcb959212f212b137066f1aa66f0bb6e86c3

scripts/launchPackager.bat

@@ -1,12 +1,12 @@
-:: Copyright (c) Facebook, Inc. and its affiliates.
-::
-:: This source code is licensed under the MIT license found in the
-:: LICENSE file in the root directory of this source tree.
-
-@echo off
-title Metro
-call .packager.bat
-cd ../../../
-node "%~dp0..\cli.js" start
-pause
-exit
+:: Copyright (c) Facebook, Inc. and its affiliates.
+::
+:: This source code is licensed under the MIT license found in the
+:: LICENSE file in the root directory of this source tree.
+
+@echo off
+title Metro
+call .packager.bat
+cd ../../../
+node "%~dp0..\cli.js" start
+pause
+exit