selftests/bpf: Migrate test_xdp_redirect.c to test_xdp_do_redirect.c

prog_tests/xdp_do_redirect.c is the only user of the BPF programs
located in progs/test_xdp_do_redirect.c and progs/test_xdp_redirect.c.
There is no need to keep both files with such close names.

Move test_xdp_redirect.c contents to test_xdp_do_redirect.c and remove
progs/test_xdp_redirect.c

Signed-off-by: Bastien Curutchet (eBPF Foundation) <bastien.curutchet@bootlin.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250110-xdp_redirect-v2-3-b8f3ae53e894@bootlin.com