Revert "Support SAML authentication (#25165)" (#29358)

This reverts #25165 (5bb8d1924d), as there
was a chance some important reviews got missed.

so after reverting this patch it will be resubmitted for reviewing again

https://github.com/go-gitea/gitea/pull/25165#issuecomment-1960670242

temporary Open #5512 again

.github/workflows/pull-db-tests.yml

@@ -37,14 +37,6 @@ jobs:
           MINIO_ROOT_PASSWORD: 12345678
         ports:
           - "9000:9000"
-      simplesaml:
-        image: allspice/simple-saml
-        ports:
-          - "8080:8080"
-        env:
-          SIMPLESAMLPHP_SP_ENTITY_ID: http://localhost:3002/user/saml/test-sp/metadata
-          SIMPLESAMLPHP_SP_ASSERTION_CONSUMER_SERVICE: http://localhost:3002/user/saml/test-sp/acs
-          SIMPLESAMLPHP_SP_SINGLE_LOGOUT_SERVICE: http://localhost:3002/user/saml/test-sp/acs
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5