#24903: Remove misleading error message to fix regression.

Before the argparse conversion, compileall would (sometimes) accept multiple
paths when -d was specified.  Afterward, it does not.  The corresponding check
in the original code claimed to prevent multiple *directories* from being
specified...but it didn't really work even to do that.  So this patch fixes
the regression by invoking the consenting adults rule: if you specify a
combination of arguments to compileall that produces files with inconsistent
destdirs (which you could do before), it is on you.

Patch by Jake Garver.