REGTEST: remove unexpected "nbthread" statement from Lua test cases

Lua test files 2 and 3 fail when threads are disabled because of a
"nbthread" statement that seems to be a leftover from an ancient
configuration. One of them even mentions a commit message showing
a reproducer not involving threads. Let's clean this up so that
running the tests without threads also works.

This should be backported to 1.9 as the problem also exists there.

reg-tests/lua/b00002.vtc

@@ -5,7 +5,6 @@ feature ignore_unknown_macro
 
 haproxy h1 -conf {
     global
-        nbthread 3
         lua-load ${testdir}/b00002.lua
         lua-load ${testdir}/b00002_print_r.lua
 

reg-tests/lua/b00003.vtc

@@ -30,7 +30,6 @@ haproxy h1 -conf {
 
     global
         lua-load ${testdir}/b00003.lua
-        nbthread 4
 
     frontend frt
         log ${Slog_addr}:${Slog_port} local0 debug err