Do not create useless indexes

Resolves: rhbz#1105465 - Please avoid to create sqlite table index in ibus-table
See: https://bugzilla.redhat.com/show_bug.cgi?id=1105465

Most of indexes which were created were not helpful at all because
most queries are done using the SQL “LIKE” operator which does
not benefit from indexes.

And the SELECT statements which do not use “LIKE” are not doing anything
where speed is critical. So we could not find a benefit in any
of the existing indexes. Benchmarking showed no significant difference
between having the indexes or not having them.

I changed the functions create_indexes() and drop_indexes() to do
nothing, if we ever find that some index is really useful, we can
easily add it again.

Not creating the indexes saves a lot of space:

Sizes with indexes:

    $ du -h -c /usr/share/ibus-table/tables/*.db
    8.6M	/usr/share/ibus-table/tables/array30-big.db
    3.7M	/usr/share/ibus-table/tables/array30.db
    3.7M	/usr/share/ibus-table/tables/cangjie-big.db
    2.1M	/usr/share/ibus-table/tables/cangjie3.db
    4.7M	/usr/share/ibus-table/tables/cangjie5.db
    572K	/usr/share/ibus-table/tables/cantonese.db
    700K	/usr/share/ibus-table/tables/cantonhk.db
    5.0M	/usr/share/ibus-table/tables/cns11643.db
    64K	/usr/share/ibus-table/tables/compose.db
    7.7M	/usr/share/ibus-table/tables/easy-big.db
    96K	/usr/share/ibus-table/tables/emoji-table.db
    6.6M	/usr/share/ibus-table/tables/erbi-qs.db
    3.0M	/usr/share/ibus-table/tables/erbi.db
    40K	/usr/share/ibus-table/tables/ipa-x-sampa.db
    640K	/usr/share/ibus-table/tables/jyutping.db
    60K	/usr/share/ibus-table/tables/latex.db
    312K	/usr/share/ibus-table/tables/mathwriter-ibus.db
    812K	/usr/share/ibus-table/tables/quick-classic.db
    2.0M	/usr/share/ibus-table/tables/quick3.db
    4.4M	/usr/share/ibus-table/tables/quick5.db
    40K	/usr/share/ibus-table/tables/rustrad.db
    5.0M	/usr/share/ibus-table/tables/scj6.db
    364K	/usr/share/ibus-table/tables/stroke5.db
    40K	/usr/share/ibus-table/tables/thai.db
    40K	/usr/share/ibus-table/tables/translit-ua.db
    40K	/usr/share/ibus-table/tables/translit.db
    40K	/usr/share/ibus-table/tables/viqr.db
    1000K	/usr/share/ibus-table/tables/wu.db
    11M	/usr/share/ibus-table/tables/wubi-haifeng86.db
    12M	/usr/share/ibus-table/tables/wubi-jidian86.db
    40K	/usr/share/ibus-table/tables/yawerty.db
    4.2M	/usr/share/ibus-table/tables/yong.db
    87M	合計

Sizes without indexes:

    $ du -h -c /usr/share/ibus-table/tables/*.db
    4.6M	/usr/share/ibus-table/tables/array30-big.db
    2.0M	/usr/share/ibus-table/tables/array30.db
    1.5M	/usr/share/ibus-table/tables/cangjie-big.db
    1020K	/usr/share/ibus-table/tables/cangjie3.db
    2.1M	/usr/share/ibus-table/tables/cangjie5.db
    236K	/usr/share/ibus-table/tables/cantonese.db
    292K	/usr/share/ibus-table/tables/cantonhk.db
    2.1M	/usr/share/ibus-table/tables/cns11643.db
    32K	/usr/share/ibus-table/tables/compose.db
    3.2M	/usr/share/ibus-table/tables/easy-big.db
    48K	/usr/share/ibus-table/tables/emoji-table.db
    3.2M	/usr/share/ibus-table/tables/erbi-qs.db
    1.3M	/usr/share/ibus-table/tables/erbi.db
    24K	/usr/share/ibus-table/tables/ipa-x-sampa.db
    268K	/usr/share/ibus-table/tables/jyutping.db
    36K	/usr/share/ibus-table/tables/latex.db
    152K	/usr/share/ibus-table/tables/mathwriter-ibus.db
    332K	/usr/share/ibus-table/tables/quick-classic.db
    980K	/usr/share/ibus-table/tables/quick3.db
    2.0M	/usr/share/ibus-table/tables/quick5.db
    24K	/usr/share/ibus-table/tables/rustrad.db
    2.2M	/usr/share/ibus-table/tables/scj6.db
    156K	/usr/share/ibus-table/tables/stroke5.db
    24K	/usr/share/ibus-table/tables/thai.db
    24K	/usr/share/ibus-table/tables/translit-ua.db
    24K	/usr/share/ibus-table/tables/translit.db
    24K	/usr/share/ibus-table/tables/viqr.db
    424K	/usr/share/ibus-table/tables/wu.db
    4.8M	/usr/share/ibus-table/tables/wubi-haifeng86.db
    5.7M	/usr/share/ibus-table/tables/wubi-jidian86.db
    24K	/usr/share/ibus-table/tables/yawerty.db
    1.8M	/usr/share/ibus-table/tables/yong.db
    40M	合計
Merge pull request #39 from mike-fabian/do-not-create-useless-indexes

Do not create useless indexes