package/libgeotiff: bump version to 1.5.1

package/libgeotiff: bump version to 1.5.1

Removed patches applied upstream:
https://github.com/OSGeo/libgeotiff/commit/2fbae8298d7cc976d7c0f329fc26dafe57fb0fc4
https://github.com/OSGeo/libgeotiff/commit/b5895ac935914f5b5c2af66f78b11d059867d71a
https://github.com/OSGeo/libgeotiff/commit/edc9ec69b43c27955ee4f24db2e6808bb1a8974d

Updated upstream URL in Config.in due to the upstream switch to github:
https://trac.osgeo.org/geotiff/

Updated license hash after upstream commit:
https://github.com/OSGeo/libgeotiff/commit/e3dd2e1bf1ce58aa98d25cc778cb491794a13197

proj 6 is now a mandatory dependency:
https://github.com/OSGeo/libgeotiff/commit/a0526817886614c41ba5fdee4a5998bafcdff658

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>