Revert "memory: simplify new (nothrow) variants"
Revert "memory: simplify new (nothrow) variants"

This reverts commit cab071627ef93d484d70c26eccc09c63b4119137.

Tomek points out that extra-large requests may still throw.

wildinto/seastar,flashbuckets/seastar,hongliangzhao/seastar,anzihenry/seastar,dwdm/seastar,scylladb/scylla-seastar,scylladb/seastar,scylladb/scylla-seastar,cloudius-systems/seastar,leejir/seastar,flashbuckets/seastar,joerg84/seastar,wildinto/seastar,cloudius-systems/seastar,shyamalschandra/seastar,chunshengster/seastar,scylladb/scylla-seastar,tempbottle/seastar,scylladb/seastar,syuu1228/seastar,jonathanleang/seastar,printedheart/seastar,xtao/seastar,hongliangzhao/seastar,bowlofstew/seastar,syuu1228/seastar,sjperkins/seastar,hongliangzhao/seastar,koolhazz/seastar,shyamalschandra/seastar,joerg84/seastar,leejir/seastar,bowlofstew/seastar,cloudius-systems/seastar,syuu1228/seastar,anzihenry/seastar,avikivity/seastar,leejir/seastar,stamhe/seastar,dwdm/seastar,wildinto/seastar,flashbuckets/seastar,dreamsxin/seastar,scylladb/seastar,anzihenry/seastar,acbellini/seastar,norcimo5/seastar,stamhe/seastar,stamhe/seastar,xtao/seastar,koolhazz/seastar,chunshengster/seastar,jonathanleang/seastar,dreamsxin/seastar,linearregression/seastar,norcimo5/seastar,avikivity/seastar,linearregression/seastar,kjniemi/seastar,xtao/seastar,sjperkins/seastar,norcimo5/seastar,tempbottle/seastar,koolhazz/seastar,kjniemi/seastar,joerg84/seastar,kjniemi/seastar,avikivity/seastar,linearregression/seastar,bowlofstew/seastar,tempbottle/seastar,printedheart/seastar,acbellini/seastar,printedheart/seastar,dreamsxin/seastar,jonathanleang/seastar,shyamalschandra/seastar,dwdm/seastar,acbellini/seastar,chunshengster/seastar,sjperkins/seastar