This broke with COPTFLAGS="-flto -O3", and so I took a look (it
complains more than normal because main isn't there). We should never
be running update-mocks except on programs expected to compile: in
this case, that's tools/test/run-test-wire.c.
Remove the code which tries to run this, which also means
non-developers won't be running update-mocks!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>