ols: Do not randomly probe serial ports

ols: Do not randomly probe serial ports

ols driver used to probe a series of available serial ports obtained
by regexp matching of common serial port names.
There are a number of problems with this approach:
1. It will probe all serial devices, including devices that do not
like to be probed, potentially causing them to act up.
2. It will try to probe serial ports which may already be opened in
other applications for other purposes.
3. It assumes the naming of the serial ports is set in stone, and
creates an unnecessary OS-specific list.
4. It produces unnecessary debug output even when an OLS device is
not connected.
5. etc...

Do not implicitly probe serial ports. Only probe the port specified
by the frontend, if any; otherwise, just quit.
Also get rid of all functionality in serial.c which was designed
specifically for random probing.

Signed-off-by: Alexandru Gagniuc <redacted>