This reverts commit 356a367eb5.
We can't use headers_sent() to determine an accurate
content length, since PHP defaults to buffering a couple of bytes
even without ob_start() (see "output_buffering" setting).
This makes the patch harmful, since it breaks any responses relying
on more structure data, like removing closing brackets from JSON.
Which in turn breaks the CMS in horrible ways (see #8010).
See #7574 for context.
The entire framework repo (with the exception of system-generated files) has been amended to respect the 120c line-length limit. This is in preparation for the enforcement of this rule with PHP_CodeSniffer.
