lua: stop trying to tweak lua's GC

cherry-picked from f0ca89ac, original author Vlada Cunat

TL;DR: I believe all lua_gc() calls stemmed from misunderstanding lua
documentation, and the current settings seem potentially dangerous.

First, let me rely on lua 5.1 docs, as luajit 2 is documented to have
done only minor changes in the GC.
http://www.lua.org/manual/5.1/manual.html#lua_gc
http://wiki.luajit.org/New-Garbage-Collector#rationale

Commit 5a709411 claims to have increased the speed of GC to 400 % of
speed of allocation, but LUA_GCSETSTEPMUL is the parameter that
controls that, and that one was lowered to 99 % and later in
0ee2d1d7 even to 50 %.  Documentation explicitly says that setting
the value under 100 % may cause problems.

The default values seem perfectly sane to me and currently I can't see
any particular reason to change them.  It's 200 % relative GC speed,
and waiting for allocated size to double before starting another cycle.

I assume the resulting possibility of GC being too slow caused the need
to explicitly force a non-incremental GC cycle once in a while, but
that seems not useful anymore and not good for latency.
26 jobs for lua_gc in 72 minutes and 36 seconds (queued for 7 seconds)
Status Job ID Name Coverage
  Build
passed #313876
amd64 linux docker
archive

00:00:42

passed #313877
amd64 linux docker
build

00:00:52

passed #313878
amd64 linux docker
build-asan

00:00:52

passed #313879
docker
kres-gen

00:00:51

 
  Test
passed #313880
docker delayed
build:darwin

00:00:41

passed #313903
amd64 linux docker
deckard

00:01:41

passed #313882
docker delayed
doc

00:01:01

passed #313883
dind
docker

00:01:49

passed #313884
docker delayed
lint:other

00:00:57

passed #313885
amd64 linux docker delayed
lint:pedantic

00:01:17

passed #313886
amd64 linux docker
lint:scan-build

00:02:30

passed #313887
amd64 linux docker
lint:tidy

00:03:29

passed #313888
amd64 linux docker
respdiff:basic

00:02:28

passed #313889
amd64 linux docker delayed
test:valgrind

00:02:09

failed #313881
amd64 linux docker
deckard

00:02:32

 
  Extended
passed #313891
respdiff
fwd-tls6-kresd.udp6

00:17:25

passed #313892
respdiff
fwd-udp6-kresd.udp6

00:23:55

passed #313896
respdiff
fwd-udp6-unbound.tcp6

01:01:57

passed #313897
respdiff
fwd-udp6-unbound.tls6

00:46:56

failed #313895
respdiff
fwd-udp6-unbound.udp6

00:31:55

passed #313894
respdiff
iter.tls6

01:07:27

passed #313893
respdiff
iter.udp6

00:41:26

passed #313890
amd64 linux docker
pytests

00:04:37

passed #313898
respdiff
resperf:fwd-tls6.udp-asan

00:07:18

passed #313899
respdiff
resperf:fwd-udp6.udp-asan

00:49:21

passed #313900
respdiff
resperf:iter.udp-asan

00:44:20

 
Name Stage Failure
failed
fwd-udp6-unbound.udp6 Extended
$ cp -t . respdiff_commitdir/*$RESPDIFF_TEST*.png ||:
$ cat respdiff_commitdir/$RESPDIFF_TEST/*histogram.tar.gz | tar -xf - -i ||:
Uploading artifacts...
Runtime platform arch=amd64 os=linux pid=126116 revision=a8a019e0 version=12.3.0
./j*: found 18 matching files

./*.png: found 2 matching files

./*histogram/*: found 6 matching files

Uploading artifacts to coordinator... ok
id=313895 responseStatus=201 Created token=V6JEimBi
ERROR: Job failed: exit status 1