Fix issue that it is not possible to remove a remote package (#803)

Resolves #802

Issue:

- Package references's setter implementation only allowed appending new elements and didn't support removing them as the `packageReferences` array is shared between both `localPackages` and `remotePackages`.

Changes:

- It checks that only the references are kept that are not part of the current type. 
- This is done by getting the object of the reference and checking the type of this reference.
- Unit test was added to verify removal case

Notes:

- To correctly remove a package, there's a few other objects and references that need to be removed _(not just the element from `packageReferences`)_

Sources/XcodeProj/Objects/Project/PBXProject.swift

@@ -137,14 +137,7 @@ public final class PBXProject: PBXObject {
     /// Remote Swift packages.
     public var remotePackages: [XCRemoteSwiftPackageReference] {
         set {
-            var finalReferences: [PBXObjectReference] = packageReferences ?? []
-            let newReferences = newValue.references()
-            for reference in newReferences {
-                if !finalReferences.contains(reference) {
-                    finalReferences.append(reference)
-                }
-            }
-            packageReferences = finalReferences
+            setPackageReferences(newValue)
         }
         get {
             packageReferences?.objects() ?? []
@@ -154,20 +147,24 @@ public final class PBXProject: PBXObject {
     /// Local Swift packages.
     public var localPackages: [XCLocalSwiftPackageReference] {
         set {
-            var finalReferences: [PBXObjectReference] = packageReferences ?? []
-            let newReferences = newValue.references()
-            for reference in newReferences {
-                if !finalReferences.contains(reference) {
-                    finalReferences.append(reference)
-                }
-            }
-            packageReferences = finalReferences
+            setPackageReferences(newValue)
         }
         get {
             packageReferences?.objects() ?? []
         }
     }
 
+    private func setPackageReferences<T: PBXContainerItem>(_ packages: [T]) {
+        let newReferences = packages.references()
+        var finalReferences: [PBXObjectReference] = packageReferences?.filter { !($0.getObject() is T) } ?? []
+        for reference in newReferences {
+            if !finalReferences.contains(reference) {
+                finalReferences.append(reference)
+            }
+        }
+        packageReferences = finalReferences
+    }
+
     /// Sets the attributes for the given target.
     ///
     /// - Parameters:

Tests/XcodeProjTests/Objects/Project/PBXProjectTests.swift

@@ -102,6 +102,46 @@ final class PBXProjectTests: XCTestCase {
                                      PBXProjError.frameworksBuildPhaseNotFound(targetName: target.name))
     }
 
+    func test_removeRemotePackage() throws {
+        // Given
+        let objects = PBXObjects(objects: [])
+
+        let buildPhase = PBXFrameworksBuildPhase(
+            files: [],
+            inputFileListPaths: nil,
+            outputFileListPaths: nil, buildActionMask: PBXBuildPhase.defaultBuildActionMask,
+            runOnlyForDeploymentPostprocessing: true
+        )
+        let target = PBXNativeTarget(name: "Target",
+                                     buildConfigurationList: nil,
+                                     buildPhases: [buildPhase])
+        objects.add(object: target)
+
+        let configurationList = XCConfigurationList.fixture()
+        let mainGroup = PBXGroup.fixture()
+        objects.add(object: configurationList)
+        objects.add(object: mainGroup)
+
+        let project = PBXProject(name: "Project",
+                                 buildConfigurationList: configurationList,
+                                 compatibilityVersion: "0",
+                                 mainGroup: mainGroup,
+                                 targets: [target])
+
+        objects.add(object: project)
+
+        let _ = try project.addSwiftPackage(repositoryURL: "url",
+                                            productName: "Product",
+                                            versionRequirement: .branch("main"),
+                                            targetName: "Target")
+
+        // When
+        project.remotePackages.removeFirst()
+
+        // Then
+        XCTAssert(project.remotePackages.isEmpty)
+    }
+
     func test_addSwiftPackage() throws {
         // Given
         let objects = PBXObjects(objects: [])