slapd.scripts-common: Avoid double-UTF8-encoding org name (Closes: #1016185)

The postinst maintscript of slapd incorrectly encodes organization names with non-ASCII characters.

The issue is that values received from debconf (already in UTF-8) are encoded once again via the function encode_utf8.

This turns

"pé" (0x70 0xC3 0xA9 = U+0070, U+00E9)

into

"pé" (0x70 0xC3 0x8e 0xC2 0xA9 = U+0070, U+00C3, U+00A9)

The are two possible scenarios:

1. If one assumes that the string returned by debconf is UTF-8 encoded (that is the case in all modern setups), then there is no need for another round of encoding.

2. If instead, one assumes that the string returned by debconf is not UTF-8 encoded, then one should also know which encoding it is in, in order to perform the right conversion.

The current code produces wrong results in both cases.