delete outdated license information
delete outdated license information

Old versions of the pyvisa documentation were released under the
Gnu FDL.  With PyVISA 1.3, Torsten switched to the MIT License.
There was a last paragraph mentioning the GFDL.
This commit fixes this.

git-svn-id: 9ab2475816adfb8420036182e3900ffc754382bd@391 516c0664-e049-0410-bc6e-8f9a6051a51d

hgrecco/pyvisa,MatthieuDartiailh/pyvisa,pyvisa/pyvisa,rubund/debian-pyvisa