Relational operators for universal integers come in three variants, e.g.:

   function "=" (Left : Uint; Right : Uint) return Boolean renames UI_Eq;
   function "=" (Left : Int;  Right : Uint) return Boolean renames UI_Eq;
   function "=" (Left : Uint; Right : Int)  return Boolean renames UI_Eq;

precisely to avoid explicit conversions with UI_From_Int, e.g.:

   if An_Uint = UI_From_Int (An_Int) then ...

This patch removes such explicit conversions. Code cleanup only;
semantics is unaffected.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* exp_ch4.adb, sem_ch13.adb, sem_eval.adb, sem_res.adb: Remove
	redundant calls to UI_From_Int.