chore(vendors): deleting/deprecating old javascript libraries

Deleted:
    calendarpopup Not even used, replaced by datepicker.
    jquery.easing Already provided by jquery ui.

Deprecated:
    jquery.autocomplete deprecated in 1.9 by jquery ui.

Fixes #6478
chore(views): renamed _elgg_views_send_page_headers() to _elgg_views_send_header_x_frame_options()

Fixes #6383
Merge pull request #6513 from sembrestels/x-frame-options

chore(views): renamed _elgg_views_send_page_headers() to _elgg_views_sen...
chore(simplecache): rationalize use of elgg_register_simplecache_view()

Since elgg_get_simplecache_url() already calls it, it has no sense call it twice.
Merge pull request #6516 from sembrestels/simplecache_view

chore(simplecache): rationalize use of elgg_register_simplecache_view()
Merge pull request #6512 from sembrestels/rm-vendors

chore(vendors): deleting/deprecating old javascript libraries