ninja&make/mac: Convert .strings files to UTF-16LE, not just UTF-16.

OS X iconv makes "UTF-16" write UTF-16BE data.  Just do the recoding in
Python, which lets "UTF-16" write UTF-16LE data (I guess it uses the host
byte order).  Also saves a subprocess invocation while here.

(Using "UTF-16LE" explicitly lets both iconv and python omit the BOM, so it's
shorter to use "UTF-16" than "UTF-16LE" and explicitly writing a BOM.)

This matches Xcode's behavior (at least Xcode 4.5).

BUG=chromium:280718
R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/23710010

git-svn-id: http://gyp.googlecode.com/svn/trunk@1707 78cadc50-ecff-11dd-a971-7dbc132099af