remove duplicate [algebra] declarations

--- a/src/HOL/Groebner_Basis.thy	Tue Mar 27 15:34:04 2012 +0200
+++ b/src/HOL/Groebner_Basis.thy	Tue Mar 27 15:34:36 2012 +0200
@@ -64,8 +64,6 @@
 declare div_by_1[algebra]
 declare mod_minus1_right[algebra]
 declare div_minus1_right[algebra]
-declare mod_div_trivial[algebra]
-declare mod_mod_trivial[algebra]
 declare mod_mult_self2_is_0[algebra]
 declare mod_mult_self1_is_0[algebra]
 declare zmod_eq_0_iff[algebra]