Fix parameter documentation in PackageDependency.swift (#7682)

* Remove mention of `nil` name which is not allowed due to the parameters being non-optional.
* Synchronize wording describing local package paths.

(cherry picked from commit 83214f0)

# Conflicts:
#	Sources/PackageDescription/PackageDependency.swift

Author: SimplyDanny

Sources/PackageDescription/PackageDependency.swift

@@ -178,8 +178,8 @@ extension Package.Dependency {
     /// packages.
     ///
     /// - Parameters:
-    ///   - name: The name of the Swift package or `nil` to deduce the name from path.
-    ///   - path: The local path to the package.
+    ///   - name: The name of the Swift package.
+    ///   - path: The file system path to the package.
     ///
     /// - Returns: A package dependency.
     @available(_PackageDescription, introduced: 5.2)