fix(macos): drop the dangling MpvMetalLayerTests reference

The Xcode project wired macos/RunnerTests/MpvMetalLayerTests.swift into
the RunnerTests target, but the file was never committed alongside it,
so the macOS test target failed to build from a clean checkout:

  error: Build input file cannot be found: .../MpvMetalLayerTests.swift
         (in target 'RunnerTests' from project 'Runner')

Remove the reference. The test it belonged to is parked on
wip/macos-drawable-size-sync together with the change it covers.

macos/Runner.xcodeproj/project.pbxproj

@@ -23,7 +23,6 @@
 /* Begin PBXBuildFile section */
 		28A54CB9141D0CB5BB3C2E50 /* Pods_Runner.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 6F93D3355F7A242CE67311F7 /* Pods_Runner.framework */; };
 		331C80D8294CF71000263BE5 /* RunnerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 331C80D7294CF71000263BE5 /* RunnerTests.swift */; };
-		B1D51A6A2F00220000000002 /* MpvMetalLayerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = B1D51A6A2F00220000000001 /* MpvMetalLayerTests.swift */; };
 		335BBD1B22A9A15E00E9071D /* GeneratedPluginRegistrant.swift in Sources */ = {isa = PBXBuildFile; fileRef = 335BBD1A22A9A15E00E9071D /* GeneratedPluginRegistrant.swift */; };
 		33CC10F12044A3C60003C045 /* AppDelegate.swift in Sources */ = {isa = PBXBuildFile; fileRef = 33CC10F02044A3C60003C045 /* AppDelegate.swift */; };
 		33CC10F62044A3C60003C045 /* MainMenu.xib in Resources */ = {isa = PBXBuildFile; fileRef = 33CC10F42044A3C60003C045 /* MainMenu.xib */; };
@@ -78,7 +77,6 @@
 		2BF8F34B75C7EEBFABBAFB4A /* Pods-Runner.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Runner.debug.xcconfig"; path = "Target Support Files/Pods-Runner/Pods-Runner.debug.xcconfig"; sourceTree = "<group>"; };
 		331C80D5294CF71000263BE5 /* RunnerTests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = RunnerTests.xctest; sourceTree = BUILT_PRODUCTS_DIR; };
 		331C80D7294CF71000263BE5 /* RunnerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RunnerTests.swift; sourceTree = "<group>"; };
-		B1D51A6A2F00220000000001 /* MpvMetalLayerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MpvMetalLayerTests.swift; sourceTree = "<group>"; };
 		333000ED22D3DE5D00554162 /* Warnings.xcconfig */ = {isa = PBXFileReference; lastKnownFileType = text.xcconfig; path = Warnings.xcconfig; sourceTree = "<group>"; };
 		335BBD1A22A9A15E00E9071D /* GeneratedPluginRegistrant.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = GeneratedPluginRegistrant.swift; sourceTree = "<group>"; };
 		33CC10ED2044A3C60003C045 /* Plezy.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = Plezy.app; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -153,7 +151,6 @@
 			isa = PBXGroup;
 			children = (
 				331C80D7294CF71000263BE5 /* RunnerTests.swift */,
-				B1D51A6A2F00220000000001 /* MpvMetalLayerTests.swift */,
 			);
 			path = RunnerTests;
 			sourceTree = "<group>";
@@ -482,7 +479,6 @@
 			buildActionMask = 2147483647;
 			files = (
 				331C80D8294CF71000263BE5 /* RunnerTests.swift in Sources */,
-				B1D51A6A2F00220000000002 /* MpvMetalLayerTests.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};