remove unneeded `Require Import` statements in rt.util

Related issue: #37

util/div_mod.v

-Require Import rt.util.ssromega rt.util.nat.
-
+Require Export rt.util.nat.
 From mathcomp Require Import ssreflect ssrbool eqtype ssrnat seq fintype bigop div.
 
 

util/minmax.v

-Require Import rt.util.tactics rt.util.notation rt.util.nat rt.util.list.
+Require Export rt.util.notation rt.util.nat rt.util.list.
 From mathcomp Require Import ssreflect ssrbool eqtype ssrnat seq fintype bigop.
 
 (* Additional lemmas about max. *)

util/nat.v

-Require Import rt.util.tactics rt.util.ssromega.
+Require Export rt.util.tactics rt.util.ssromega.
 From mathcomp Require Import ssreflect ssrbool eqtype ssrnat seq fintype bigop div.
 
 (* Additional lemmas about natural numbers. *)

util/nondecreasing.v

-Require Import rt.util.epsilon.
-Require Import rt.util.nat.
-Require Import rt.util.list.
-Require Import rt.util.tactics.
-Require Import rt.util.ssromega.
+Require Export rt.util.epsilon.
+Require Export rt.util.nat.
+Require Export rt.util.list.
 From mathcomp Require Import ssreflect ssrbool ssrfun eqtype ssrnat seq fintype bigop.
 
 (** * Non-Decreasing Sequence and Distances *)

util/sum.v

-Require Import rt.util.tactics.
-Require Import rt.util.notation.
-Require Import rt.util.nat.
-Require Import rt.util.ssromega.
+Require Export rt.util.notation.
+Require Export rt.util.nat.
 
 From mathcomp Require Import ssreflect ssrbool eqtype ssrnat seq fintype bigop path.