Hg encoding fix for commit

Don't pass "--encoding" to the commit command. Default encoding is fine: it is cp1251/UTF-8 for Win/Unix or HGENCODING if it is set: being set for IDEA it is inherited by the hg process spawned by IDEA.
Together with 7eab3d8f8f it fixes IDEA-67158.

Remove redundant HgEncodingUtil.getDefaultCharsetName
Add javadocs and @NotNulls

plugins/hg4idea/src/org/zmlx/hg4idea/command/HgCommitCommand.java

@@ -66,8 +66,6 @@ public class HgCommitCommand {
     for (HgFile hgFile : myFiles) {
       parameters.add(hgFile.getRelativePath());
     }
-    parameters.add("--encoding");
-    parameters.add(HgEncodingUtil.getDefaultCharsetName());
 
     ensureSuccess(new HgCommandExecutor(myProject).executeInCurrentThread(myRoot, "commit", parameters));
     final MessageBus messageBus = myProject.getMessageBus();

plugins/hg4idea/src/org/zmlx/hg4idea/util/HgEncodingUtil.java

@@ -16,14 +16,19 @@ public class HgEncodingUtil {
   private HgEncodingUtil() {
   }
 
+  /**
+   * Returns the default charset for Mercurial.
+   * It is cp1251 for Windows, and UTF-8 for Unix-like systems.
+   * The {@code HGENCODING} environment variable is not considered, because being set for IDEA it is inherited by the hg process
+   * spawned by IDEA.
+   * @return cp1251 for windows / UTF-8 for Unix-like systems.
+   */
+  @NotNull
   public static Charset getDefaultCharset() {
     return SystemInfo.isWindows ? getCharsetForNameOrDefault(WINDOWS_DEFAULT_CHARSET) : getCharsetForNameOrDefault(UNIX_DEFAULT_CHARSET);
   }
-  
-  public static String getDefaultCharsetName() {
-    return SystemInfo.isWindows ? WINDOWS_DEFAULT_CHARSET : UNIX_DEFAULT_CHARSET;
-  }
 
+  @NotNull
   private static Charset getCharsetForNameOrDefault(@NotNull String name) {
     try {
       return Charset.forName(name);
@@ -32,5 +37,4 @@ public class HgEncodingUtil {
       return Charset.defaultCharset();
     }
   }
-  
 }