[Docs] Update painless-lang-spec.asciidoc (#29425)
[Docs] Update painless-lang-spec.asciidoc (#29425)

Remove redundant word.
gfyoung/elasticsearch,GlenRSmith/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,rajanm/elasticsearch,robin13/elasticsearch,rajanm/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,rajanm/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,rajanm/elasticsearch,GlenRSmith/elasticsearch,HonzaKral/elasticsearch,gfyoung/elasticsearch,gfyoung/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,nknize/elasticsearch,rajanm/elasticsearch,nknize/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,HonzaKral/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,rajanm/elasticsearch,gingerwizard/elasticsearch,coding0011/elasticsearch,robin13/elasticsearch,HonzaKral/elasticsearch,gfyoung/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch