scripts: Remove unused variables in all Python scripts

Discovered with pylint3.

Use the placeholder name '_' for unproblematic unused variables. It's
what I'm used to, and pylint knows not to flag it.

Python tip:

    for i in range(n):
        some_list.append(0)

can be replaced with

    some_list += n*[0]

Similarly, 3*'\t' gives '\t\t\t'.

(Relevant here because pylint flagged the loop index as unused.)

To do integer division in Python 3, use // instead of /.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

scripts/gen_priv_stacks.py

@@ -79,14 +79,14 @@ def write_gperf_table(fp, eh, objs):
     # priv stack declarations
     fp.write("%{\n")
     fp.write(includes)
-    for obj_addr, ko in objs.items():
+    for obj_addr in objs:
         fp.write(priv_stack_decl_temp % (obj_addr))
     fp.write("%}\n")
 
     # structure declaration
     fp.write(structure)
 
-    for obj_addr, ko in objs.items():
+    for obj_addr in objs:
         byte_str = struct.pack("<I" if eh.little_endian else ">I", obj_addr)
         fp.write("\"")
         for byte in byte_str: