Clean up recent string conversion function changes, part 1: Remove unnecessary code.  Thanks to a change in escape.cc I can basically revert the ICU conversions back to what they used to be; I can also get rid of half the conversions immediately since they aren't used.

This does not split out the "adjust" versions of the UTF conversions into their own header/implementation; that's coming in the next patch.

BUG=4010
TEST=none
Review URL: http://codereview.chromium.org/380007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@31533 0039d316-1c4b-4281-b951-d872f2087c98

• base/i18n/icu_string_conversions.cc[diff]
• base/i18n/icu_string_conversions.h[diff]
• base/i18n/icu_string_conversions_unittest.cc[diff]
• base/utf_string_conversions.cc[diff]
• base/utf_string_conversions.h[diff]
• base/utf_string_conversions_unittest.cc[diff]
• net/base/escape.cc[diff]