Remove unused and unread variables reported by cppcheck

[rcorsi]

I found these unused variables by using the cppcheck tool.

[rcorsi]

Here is a command line to see the already reported unused variables. I'm using cppcheck 1.19 on Ubuntu 26.04

$ cppcheck --enable=style *.c 2>&1 | grep -A 2 unusedVariable
drivewire.c:120:7: style: Unused variable: buffer [unusedVariable]
 char buffer[81];
      ^
drivewire.c:195:9: style: Unused variable: i [unusedVariable]
    int i;
        ^
--
dwprotocol.c:11:10: style: Unused variable: rfds [unusedVariable]
  fd_set rfds;
         ^
dwprotocol.c:12:18: style: Unused variable: tv [unusedVariable]
  struct timeval tv;
                 ^

I was digging a little more and found a few unreadVariables too. I'll update the PR to include these too.

$ cppcheck --enable=style *.c 2>&1 | grep -A 2 unreadVariable
dwprotocol.c:13:9: style: Variable 'timeString' is assigned a value that is never used. [unreadVariable]
  char *timeString = NULL;
        ^
--
dwwin.c:10:8: style: Variable 'y' is assigned a value that is never used. [unreadVariable]
 int y = 1;
       ^
dwwin.c:10:6: style: Variable 'y' is assigned a value that is never used. [unreadVariable]
 int y = 1;
     ^