slider: fix slider for tizen 3.0 GUI guide, elm_prefs: add @internal

slider: fix slider for tizen 3.0 GUI guide, elm_prefs: add @internal

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    slider: fix slider for tizen 3.0 GUI guide.

    - deleted unnecessary vector objects.
    - change slider indicator initial value.

    Signed-off-by: Hosang Kim <hosang12.kim@samsung.com>
    Change-Id: Ib05f483e2d3f362294bed5ab280327bd27022d76

    Original commit: 07fb895f70cc65d4ec3681fdc12fe9f739cf76f5
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    elm_prefs: add @internal to defgroup not to show in document

    Signed-Off-By: Jee-Yong Um <jc9.um@samsung.com>
    Change-Id: Id68f0880657284cfbc8a80ccfafd7793690dabf0

    Original commit: c616c666a14f326cdb193b3ec6a3cab2fcc27382
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Change-Id: I8fd1e776ee3305d4c67e856b362e177ead714470