fix a mis-encoding in three tests

Three wrongly hand-crafted bit-vector constants are fixed.  Bit-vector
constants are hex, and must not use leading zeros.

Author: kroening

regression/symtab2gb/multiple_symtabs/entry_point.json_symtab

@@ -1000,7 +1000,7 @@
                     }
                   },
                   "value": {
-                    "id": "00000000000000000000000000000000",
+                    "id": "0",
                     "sub": [
                     ],
                     "namedSub": {

regression/symtab2gb/single_symtab/entry_point.json_symtab

@@ -809,7 +809,7 @@
                     }
                   },
                   "value": {
-                    "id": "00000000000000000000000000000000",
+                    "id": "0",
                     "sub": [
                     ],
                     "namedSub": {

unit/solvers/smt2_incremental/encoding/struct_encoding.cpp

@@ -414,7 +414,7 @@ TEST_CASE("decoding into struct expressions.", "[core][smt2_incremental]")
      from_integer(2, unsignedbv_typet{16}),
      from_integer(1, signedbv_typet{24})},
     struct_tag};
-  const exprt encoded = constant_exprt{"000000030002000001", bv_typet{72}};
+  const exprt encoded = constant_exprt{"30002000001", bv_typet{72}};
   REQUIRE(test.struct_encoding.decode(encoded, struct_tag) == expected);
 }