scripts: Remove setting of PATH from functions file

scripts: Remove setting of PATH from functions file

The current setting is inconsistent with settings on most systems,
putting /bin before /sbin.  Use of /usr/local/bin, which may be
required on some systems, is also overridden.  This can make it
difficult to do interactive debugging of script problems.

Rely on the system PATH instead.

If system-specific changes need to be made then this can be done in a
configuration file.

Signed-off-by: Martin Schwenke <martin@meltin.net>