mathlib3

c8771b6b - fix(algebra/ring/basic): delete mul_self_sub_mul_self_eq (#4119)

fix(algebra/ring/basic): delete mul_self_sub_mul_self_eq (#4119) It's redundant with `mul_self_sub_mul_self`. Also renamed `mul_self_sub_one_eq` to `mul_self_sub_one`.