Here's what Laura's "There are no more guns in the valley" eulogy means in Logan. Hugh Jackman was a virtual unknown when he was cast in the original X-Men. Actors such as Russell Crowe passed on the part before Dougray Scott was cast. Unfortunately, Scott's shooting schedule on John Woo's Mission: Impossible II overlapped, so Jackman was hired at the last moment. Despite controversy from fans about the actor being too tall and not wearing Wolverine's trademark yellow outfit, he proved to be perfect casting.
Jackman would go on to play the role in a further 8 movies and a number of video games, including the X-Men Origins: Wolverine tie-in. He decided to bow out as the character with Logan in 2017 which ended with the character's demise. Logan was a real surprise to both fans and critics, being a violent, emotional, R-rated drama. The movie depicted a world where mutants were dying out and Wolverine is looking after a sick Professor X (Patrick Stewart), whilst also learning to take care for his young clone/daughter Laura (Dafne Keen).
Logan director James Mangold had previously directed The Wolverine and was frustrated with how the sequel turned out. He felt the parts focusing on Logan as a character worked best, while the overt comic book moments, such as the Silver Samurai battle, hurt the final product. This is why he focused on making Logan a more mature project and chose classic western Shane as a tonal model. There are direct parallels between Logan and Shane, including title characters who wish for a peaceful life but have been tainted by violence. Laura also watches Shane on TV with Professor X, which plays a major role in the final scene.
Logan is fatally wounded in a battle with his own clone X-24 in the finale and succumbs to his wounds holding Laura's hand. After he's buried she gives a eulogy at his grave that directly quotes the final speech from Shane, including the key phrase "There are no more guns in the valley." Logan may have killed the bad guys but it came at the cost of his life, while Shane killed the villains but decided to leave, feeling his life is marked by violence and he'll only hurt the people he cares about if he stays.
Logan's "There are no more guns in the valley" speech means that now the villains are defeated, Laura has a chance to turn away from the violence that has marked her and Wolverine's lives. She may have killed to survive but she doesn't have to be defined by it like her father was. Logan didn't get to ride off into the sunset but at least he died knowing his daughter had a chance to lead the life he could never have.
While Logan initially toned down the links to the X-Men movies, it ends with the nice touch of Laura turning his grave marker to the side to create an X. "There are no more guns in the valley" is an emotional scene in Logan, with the dual purpose of Laura saying goodbye to her father and fans saying goodbye to Hugh Jackman's Wolverine.