[PlaygroundRuntime] Removed the prototype version of what became CustomPlaygroundDisplayConvertible.

`CustomPlaygroundDisplayConvertible` now exists in the standard library, so there's no need to provide this prototype version in PlaygroundRuntime.
This was only present for easy testing in PlaygroundLogger before the real protocol was created and available for use.

Author: cwakamo

Experimental/PlaygroundRuntime/PlaygroundRuntime.xcodeproj/project.pbxproj

@@ -7,13 +7,11 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
-		5E26461C1FB6471B002DC6B6 /* PlaygroundQuickLookPrototype.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5E26461B1FB6471B002DC6B6 /* PlaygroundQuickLookPrototype.swift */; };
 		5EB7829A1FAE6CD700ADE84E /* PlaygroundTransformRuntime.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5EB782991FAE6CD700ADE84E /* PlaygroundTransformRuntime.swift */; };
 		5EEA48FA1FAFD9920020682B /* PCMacroRuntime.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5EEA48F91FAFD9920020682B /* PCMacroRuntime.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
-		5E26461B1FB6471B002DC6B6 /* PlaygroundQuickLookPrototype.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PlaygroundQuickLookPrototype.swift; sourceTree = "<group>"; };
 		5EB7828B1FAE6B6F00ADE84E /* PlaygroundRuntime.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = PlaygroundRuntime.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		5EB7828F1FAE6B6F00ADE84E /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		5EB782991FAE6CD700ADE84E /* PlaygroundTransformRuntime.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PlaygroundTransformRuntime.swift; sourceTree = "<group>"; };
@@ -52,7 +50,6 @@
 			children = (
 				5EB782991FAE6CD700ADE84E /* PlaygroundTransformRuntime.swift */,
 				5EEA48F91FAFD9920020682B /* PCMacroRuntime.swift */,
-				5E26461B1FB6471B002DC6B6 /* PlaygroundQuickLookPrototype.swift */,
 				5EB7829F1FAE777900ADE84E /* Supporting Files */,
 			);
 			path = PlaygroundRuntime;
@@ -147,7 +144,6 @@
 			buildActionMask = 2147483647;
 			files = (
 				5EEA48FA1FAFD9920020682B /* PCMacroRuntime.swift in Sources */,
-				5E26461C1FB6471B002DC6B6 /* PlaygroundQuickLookPrototype.swift in Sources */,
 				5EB7829A1FAE6CD700ADE84E /* PlaygroundTransformRuntime.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;