[otbn] Remove duplicated assignments in decoder

These both appear a few lines earlier in the same block.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>

hw/ip/otbn/rtl/otbn_decoder.sv

diff --git a/hw/ip/otbn/rtl/otbn_decoder.sv b/hw/ip/otbn/rtl/otbn_decoder.sv
index 067698a..4d3b042 100644
--- a/hw/ip/otbn/rtl/otbn_decoder.sv
+++ b/hw/ip/otbn/rtl/otbn_decoder.sv
@@ -559,7 +559,6 @@
             rf_ren_b_base        = 1'b1;
             rf_wdata_sel_bignum  = RfWdSelLsu;
             rf_d_indirect_bignum = 1'b1;
-            ld_insn              = 1'b1;
 
             if (insn[8]) begin
               a_wlen_word_inc_bignum = 1'b1;
@@ -582,7 +581,6 @@
             rf_ren_a_base        = 1'b1;
             rf_ren_b_base        = 1'b1;
             rf_ren_b_bignum      = 1'b1;
-            st_insn              = 1'b1;
             rf_b_indirect_bignum = 1'b1;
 
             if (insn[8]) begin