libassuan: Fix license

libassuan: Fix license

libassuan license is wrong since the addition of the package in commit
https://git.openwrt.org/?p=feed/packages.git;a=commit;h=e24e8fa98c813911419271d64433deb2b453fa02

Indeed, libassuan has been licensed under LGPL-2.1+ since version 1.0.3
back in 2007 [1]:

Noteworthy changes in version 1.0.3 (2007-08-24)
------------------------------------------------

 * Changed the license of the library code back to LGPLv2.1 to support
   a bunch of GPLv2(only) software which does not allow the use of
   LGPLv3.  Note that this is only a temporary change and authors of
   GPLv2(only) software are asked to switch to GPLv3 or to add an
   exception which allow the use of LPGLv3 software.

[1]: https://git.gnupg.org/cgi-bin/gitweb.cgi?p=libassuan.git;a=blob;f=NEWS;h=3a86eca4175fbcb12bb00722c2047062df67a46d;hb=HEAD

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>