bug#27927: 25.2; Doc string of `region-extract-function'

[Drew Adams]

This doc string now reads a bit like a kludge was added to what was
there before.  There is nothing that should now favor the meaning of the
argument as "delete".  The parameter should be renamed from DELETE to
just ACTION or ARG (or something else).

"If DELETE is `delete-only'...
 If DELETE is nil...
 If DELETE is `bounds', then don't delete, but..."

Change that to something like

"If ACTION is `delete-only'...
 If ACTION is nil...
 If ACTION is `bounds'...

In GNU Emacs 25.2.1 (x86_64-w64-mingw32)
 of 2017-04-24 built on LAPHROAIG
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Configured using:
 'configure --without-dbus --without-compress-install 'CFLAGS=-O2
 -static -g3''