more unused private members removed

Please double check the "never been used" items, especially if the
authors are still available.

ServiceBrowser::m_usingContextView has been left over since
dd303617dd2cf0c0113f710660df78fba38421d6

SqlPodcastEpisode::m_batchUpdate has never been used since its
introduction in 680b5102d0f9f011ec993d5277b3a9b417848443

Transcoding::AssistantDialog::m_defaultEncoder has never been used
(introduced in 1a0287f7925d92a05a530ab83fffbc9afae67e86)

AppletToolbarAppletItem::m_labelPadding left over after
568bfcb808ad43bfad39b20441a291a6392f4092

LikeBackDialog::m_requestNumber_ unused in the library imported in
f4683691c5ddc692de2f3ccf54f4d8316c807c4c

DynamicView::m_expandToggledWhenPressed _was_ used, but the code has
always been commented out since 40b768ec4a08d23dceea8f72df1c601574614081
and removed completely in 2fe7dd743c66b2fb9f9a6bbb7b2d50730a843056

Daap::Reader::m_loadedTracks has never been used since patch of
382d427f87f6702a5431b325c56be3b79de45b6c

OpmlDirectoryMetaFactory::m_service never used (introduced in
19eb9efe689628de819842487fde489bddaca13b)