Remove test-longjmp.c (#3188)

The test is not needed anymore.
This file was added back then, when our libc had its own longjump implementation.
Now with this test we are only testing the system's longjump implementation which -in fact- works great.

JerryScript-DCO-1.0-Signed-off-by: Daniel Balla [email protected]

Author: Daniel Balla