Remove unused setting SECURE_BROWSER_XSS_FILTER

From docs:

Most modern browsers don't honor the ``X-XSS-Protection`` HTTP header. You can
use Content-Security-Policy without allowing ``'unsafe-inline'`` scripts instead.

bedrock/settings/base.py

@@ -648,7 +648,6 @@ def get_app_name(hostname):
 SECURE_REFERRER_POLICY = config("SECURE_REFERRER_POLICY", default="strict-origin-when-cross-origin")
 SECURE_HSTS_SECONDS = config("SECURE_HSTS_SECONDS", default="0", parser=int)
 SECURE_HSTS_INCLUDE_SUBDOMAINS = False
-SECURE_BROWSER_XSS_FILTER = config("SECURE_BROWSER_XSS_FILTER", default="true", parser=bool)
 SECURE_CONTENT_TYPE_NOSNIFF = config("SECURE_CONTENT_TYPE_NOSNIFF", default="true", parser=bool)
 SECURE_SSL_REDIRECT = config("SECURE_SSL_REDIRECT", default=str(not DISABLE_SSL), parser=bool)
 SECURE_REDIRECT_EXEMPT = [