package/libssh: bump to version 0.8.7

Drop upstream patch.

Fixes strict-overflow build error with older toolchains.

Fixes:
http://autobuild.buildroot.net/results/b95b1939a55111fc6b90ef253a32402b87f9c4ab/
http://autobuild.buildroot.net/results/281cb7b940178e4fe98940ddeed07ad546b23931/
http://autobuild.buildroot.net/results/e95d5957c19ff01120903a66d1167279a34da2ce/



Cc: Scott Fan <fancp2007@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>