MappingConfiguration: Remove optimised merged v2 code path

This was leaving the broken "intermediary, named, official"
namespace order from layered mappings. While it could've been
fixed there, the optimised code path also lacked some fixes
to enclosing classes from MappingsMerger, so it's better to
use the "vanilla" code from Fabric.

src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingConfiguration.java

@@ -37,16 +37,15 @@
 import java.nio.file.StandardCopyOption;
 import java.nio.file.StandardOpenOption;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 
-import org.apache.tools.ant.util.StringUtils;
 import com.google.common.base.Stopwatch;
 import com.google.gson.JsonObject;
 import dev.architectury.loom.util.MappingOption;
+import org.apache.tools.ant.util.StringUtils;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
 import org.jetbrains.annotations.Nullable;
@@ -69,8 +68,8 @@
 import net.fabricmc.loom.util.ZipUtils;
 import net.fabricmc.loom.util.service.ScopedSharedServiceManager;
 import net.fabricmc.loom.util.service.SharedServiceManager;
-import net.fabricmc.loom.util.srg.MCPReader;
 import net.fabricmc.loom.util.srg.ForgeMappingsMerger;
+import net.fabricmc.loom.util.srg.MCPReader;
 import net.fabricmc.loom.util.srg.SrgNamedWriter;
 import net.fabricmc.mappingio.MappingReader;
 import net.fabricmc.mappingio.format.MappingFormat;
@@ -334,12 +333,7 @@ private void storeMappings(Project project, SharedServiceManager serviceManager,
 			extractExtras(delegate.fs());
 		}
 
-		if (areMappingsMergedV2(baseTinyMappings)) {
-			// Architectury Loom Patch
-			// If a merged tiny v2 mappings file is provided
-			// Skip merging, should save a lot of time
-			Files.copy(baseTinyMappings, tinyMappings, StandardCopyOption.REPLACE_EXISTING);
-		} else if (areMappingsV2(baseTinyMappings)) {
+		if (areMappingsV2(baseTinyMappings)) {
 			// These are unmerged v2 mappings
 			IntermediateMappingsService intermediateMappingsService = IntermediateMappingsService.getInstance(serviceManager, project, minecraftProvider);
 
@@ -406,17 +400,6 @@ private static boolean areMappingsV2(Path path) throws IOException {
 		}
 	}
 
-	private static boolean areMappingsMergedV2(Path path) throws IOException {
-		try (BufferedReader reader = Files.newBufferedReader(path)) {
-			reader.mark(4096); // == DETECT_HEADER_LEN
-			boolean isTinyV2 = MappingReader.detectFormat(reader) == MappingFormat.TINY_2_FILE;
-			reader.reset();
-			return isTinyV2 && MappingReader.getNamespaces(reader, MappingFormat.TINY_2_FILE).containsAll(Arrays.asList("named", "intermediary", "official"));
-		} catch (NoSuchFileException e) {
-			return false;
-		}
-	}
-
 	public static void extractMappings(Path jar, Path extractTo) throws IOException {
 		try (FileSystemUtil.Delegate delegate = FileSystemUtil.getJarFileSystem(jar)) {
 			extractMappings(delegate.fs(), extractTo);