Remove duplicated 'charset' in Content-Type header for Javascript files

[jorti]

Javascript files are served over HTTP with an incorrect Content-Type header because the 'charset' option is duplicated:

$ curl -I http://127.0.0.1:8083/static/js/table.js
HTTP/1.1 200 OK
Content-Disposition: inline; filename=table.js
Content-Type: text/javascript; charset=UTF-8; charset=utf-8
Content-Length: 35967
Last-Modified: Sat, 16 Nov 2024 06:21:28 GMT
Cache-Control: no-cache
ETag: "1731738088.0-35967-471731799"
Date: Sat, 08 Feb 2025 16:30:42 GMT
Content-Security-Policy: default-src 'self' 'unsafe-inline' 'unsafe-eval'; font-src 'self' data:; img-src 'self' data:; object-src 'none';
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Strict-Transport-Security: max-age=31536000

This header is not RFC 1521 compliant and it's breaking some reverse proxy setups that perform compression. See this bug for reference:

crocodilestick/Calibre-Web-Automated#217