wikibits: Remove methods deprecated since 1.17 and 1.18

wikibits: Remove methods deprecated since 1.17 and 1.18

Keeping only importScript and friends and addOnloadHook for now.

Inline wikiUrlencode logic so that the dependency on mediawiki.util can be
removed, which caused significant performance overhead (See I54f087655e1c).

Follows-up:
* 68fae478a8 (1.22; deprecation warnings for ua vars)
* ec69391a4f (1.22; deprecation warnings for jsMsg)
* fcf4934a52 (1.23; deprecation warnings for the rest)

The following have been deprecated since either 1.17 or 1.18. Deprecation
warnings were added in 1.22. Most of these variables have also been replaced
with dummy placeholders in 1.22 so that calling code is silently disabled
instead of causing cascading failures into other code. Anything still using
these variables to date has been broken since at least April 2013.

* User-Agent variables:
  is_gecko, is_chrome_mac, is_chrome, webkit_version, is_safari_win, is_safari,
  webkit_match, is_ff2, ff2_bugs, is_ff2_win, is_ff2_x11, opera95_bugs,
  opera7_bugs, opera6_bugs, is_opera_95, is_opera_preseven, is_opera, ie6_bugs.
  (deprecated since 1.17; warnings and hardcoded to false since 1.22)
  clientPC
  (deprecated since 1.17; warnings added in 1.22)

* DOM manipulation:
  changeText, killEvt, addHandler, hookEvent, addClickHandler, removeHandler,
  getElementsByClassName, getInnerText.
  (deprecated since 1.17; replaced with no-op warning dummies in 1.22)

* Checkbox utilities:
  setupCheckboxShiftClick, addCheckboxClickHandlers.
  (deprecated since 1.17; replaced with no-op warning dummies in 1.22)

* Classic toolbar utilities:
  mwEditButtons, mwCustomEditButtons
  (deprecated since 1.17; replaced with no-op warning dummies in 1.22)

* Misc utilities:
  - injectSpinner, removeSpinner, escapeQuotes, escapeQuotesHTML, jsMsg
    (deprecated since 1.17; replaced with no-op warning dummies in 1.22)
  - addPortletLink, appendCSS, tooltipAccessKeyPrefix,
    tooltipAccessKeyRegexp, updateTooltipAccessKeys
    (deprecated since 1.17; warnings added in 1.22)

Bug: T122755
Change-Id: I7f9f61ea81ad1efa0b5cff79b5e5f4bbe2d401fe