Copyright: small updates

The I binding was removed from input.conf (although it's probably not
copyrightable, but still).

bootstrap.py has a bunch of authors which probably make the licensing
situation a pain - but it's not integral part of the build system or the
source code, so it doesn't matter for a LGPL core.

I checked and cleaned up the build system in the last few commits. There
was the possibility that parts of it were based on actual code of the
old "configure" file, in particular with the waftools/fragments/ files
(it turned out some were, some even not covered by LGPL agreements).
This was checked, so I'm confident only the commit mentioned in the
Copyright file holds back proper LGPL licensing of it. (And I guess I
have to wait for a reply.)

I checked the English translations. There used to be help_mp-en.h (or
help_mp.h earlier), which was part of the source code, and which
contained most terminal and GUI messages. This was done for the purpose
of localization, but all localizations were dropped at one point in
mplayer2 development. At this point, the message defines were moved back
to the source code. (While in the years before that, they were moved
from the source code to the file where applicable.) I didn't check
help_mp-en.h when it was merged back. There was the possibility that
someone might have changed one of the English messages (i.e. added his
copyright to it), which then was copied back to the source code, without
accounting for that copyright. Upon checking the history now, it seems
this didn't happen for any code that we want to relicense to LGPL (in
fact, it happened to some messages in the DVD code only).

Copyright

@@ -32,14 +32,15 @@ Some libraries are GPLv2+ or GPLv3+ only. Building mpv with Samba support makes
 it GPLv3+.
 
 Source files with specific licenses:
-- etc/input.conf is LGPLv2.1+ (possible exception with I key binding)
+- etc/input.conf is LGPLv2.1+
 - etc/builtin.conf is LGPLv2.1+
 - etc/encoding-profiles.conf is LGPLv2.1+
 - everything else under etc/ is unknown
 - everything under DOCS/man/ is GPLv2+
 - sub/osd_font.otf is LGPLv2.1+
-- some tests under waftools/fragments/ might be GPLv2+
 - version.sh is LGPLv2+
+- bootstrap.py is unknown (probably GPLv2+ or LGPLv2+)
+- wscript: GPLv2+ (due to 98fca3531841221b)
 
 Some files are marked with "Almost LGPL." These files are GPL, but all authors
 have agreed to relicense them to LGPL. the problem is that one of the authors is
@@ -350,6 +351,4 @@ x   player/video.c                  extremely hard
     video/vt.*                      LGPL
 
 Other:
-x   Build system                    nominally LGPL, but might contain GPL traces
-x   English translations            removed, but traces might be in C code
 x   Logo                            GPL (?), might have to exclude from LGPL builds