switch mmlu variants over to using

lm_eval/tasks/mmlu/generative/mmlu_sociology.yaml

 "dataset_name": "sociology"
 "description": "The following are multiple choice questions (with answers) about sociology.\n\
   \n"
-"group": "mmlu_social_sciences_generative"
-"group_alias": "social_sciences"
+"tag": "mmlu_social_sciences_generative"
 "include": "_default_template_yaml"
 "task": "mmlu_sociology_generative"
 "task_alias": "sociology"

lm_eval/tasks/mmlu/generative/mmlu_us_foreign_policy.yaml

 "dataset_name": "us_foreign_policy"
 "description": "The following are multiple choice questions (with answers) about us\
   \ foreign policy.\n\n"
-"group": "mmlu_social_sciences_generative"
-"group_alias": "social_sciences"
+"tag": "mmlu_social_sciences_generative"
 "include": "_default_template_yaml"
 "task": "mmlu_us_foreign_policy_generative"
 "task_alias": "us_foreign_policy"

lm_eval/tasks/mmlu/generative/mmlu_virology.yaml

 "dataset_name": "virology"
 "description": "The following are multiple choice questions (with answers) about virology.\n\
   \n"
-"group": "mmlu_other_generative"
-"group_alias": "other"
+"tag": "mmlu_other_generative"
 "include": "_default_template_yaml"
 "task": "mmlu_virology_generative"
 "task_alias": "virology"

lm_eval/tasks/mmlu/generative/mmlu_world_religions.yaml

 "dataset_name": "world_religions"
 "description": "The following are multiple choice questions (with answers) about world\
   \ religions.\n\n"
-"group": "mmlu_humanities_generative"
-"group_alias": "humanities"
+"tag": "mmlu_humanities_generative"
 "include": "_default_template_yaml"
 "task": "mmlu_world_religions_generative"
 "task_alias": "world_religions"