feat: DEPR USE-JWT-COOKIE header

his repo is no longer using USE-JWT-COOKIE header,
since it has the required edx-drf-extensions>10.2.0,
where it was fully removed.

This is final clean-up for this repo.

See "[DEPR]: USE-JWT-COOKIE header" for more details:
- openedx/edx-drf-extensions#371

edx_exams/settings/base.py

@@ -86,9 +86,7 @@ def root(*path_fragments):
 
 # Enable CORS
 CORS_ALLOW_CREDENTIALS = True
-CORS_ALLOW_HEADERS = corsheaders_default_headers + (
-    'use-jwt-cookie',
-)
+CORS_ALLOW_HEADERS = corsheaders_default_headers
 CORS_ORIGIN_WHITELIST = []
 
 ROOT_URLCONF = 'edx_exams.urls'