examples/x11.c: remove dead assigments of some return values
examples/x11.c: remove dead assigments of some return values

Detected by clang scan in line 212, column 9.
Detected by clang scan in line 222, column 13.
Detected by clang scan in	line 410, column 13.

libssh2/libssh2,libssh2/libssh2,libssh2/libssh2,libssh2/libssh2