Revert "In sat: 'x' in init attr should not override constant"

This reverts commit 2b37a093e9.

tests/sat/initval.v

@@ -1,7 +1,6 @@
 module test(input clk, input [3:0] bar, output [3:0] foo);
   reg [3:0] foo = 0;
   reg [3:0] last_bar = 0;
-  reg [3:0] asdf = 4'b1xxx;
 
   always @*
     foo[1:0] <= bar[1:0];
@@ -12,8 +11,5 @@ module test(input clk, input [3:0] bar, output [3:0] foo);
   always @(posedge clk)
     last_bar <= bar;
 
-  always @*
-    asdf[2:0] <= 3'b111;
-
   assert property (foo == {last_bar[3:2], bar[1:0]});
 endmodule

tests/sat/initval.ys

@@ -1,4 +1,4 @@
 read_verilog -sv initval.v
-proc;
+proc;;
 
 sat -seq 10 -prove-asserts