ORC-1569: Remove HadoopShimsPre2_3, HadoopShimsPre2_6, HadoopShimsPre…

…2_7 classes

### What changes were proposed in this pull request?

This PR aims to remove `HadoopShimsPre2_3`, `HadoopShimsPre2_6`, `HadoopShimsPre2_7` classes and use `HadoopShimsCurrent` always.

### Why are the changes needed?

1. `HadoopShimsCurrent` supports not only Apache Hadoop 3+ but also Apache Hadoop 2.7+.

2. Apache ORC 2.0 uses Hadoop 3.x shaded client doesn't need old shims for Hadoop 2.6 and olders.
    - #1509

In addition, Apache Spark community also has been using the shaded Hadoop client since Spark 3.2 (SPARK-33212) and dropped `Hadoop 2` profile via [SPARK-42452](https://issues.apache.org/jira/browse/SPARK-42452) completely at Spark 3.5.0.

### How was this patch tested?

Pass the CIs.

Closes #1724 from dongjoon-hyun/ORC-1569.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: William Hyun <william@apache.org>

java/core/src/java/org/apache/orc/impl/HadoopShimsFactory.java

@@ -32,11 +32,6 @@ public class HadoopShimsFactory {
 
   private static final String CURRENT_SHIM_NAME =
       "org.apache.orc.impl.HadoopShimsCurrent";
-  private static final String PRE_2_6_SHIM_NAME =
-      "org.apache.orc.impl.HadoopShimsPre2_6";
-  private static final String PRE_2_7_SHIM_NAME =
-      "org.apache.orc.impl.HadoopShimsPre2_7";
-
   private static HadoopShims SHIMS = null;
 
   private static HadoopShims createShimByName(String name) {
@@ -57,18 +52,9 @@ public static synchronized HadoopShims get() {
       int major = Integer.parseInt(versionParts[0]);
       int minor = Integer.parseInt(versionParts[1]);
       if (major < 2 || (major == 2 && minor < 7)) {
-        LOG.warn("Hadoop " + VersionInfo.getVersion() + " support is deprecated. " +
-            "Please upgrade to Hadoop 2.7.3 or above.");
-      }
-      if (major < 2 || (major == 2 && minor < 3)) {
-        SHIMS = new HadoopShimsPre2_3();
-      } else if (major == 2 && minor < 6) {
-        SHIMS = createShimByName(PRE_2_6_SHIM_NAME);
-      } else if (major == 2 && minor < 7) {
-        SHIMS = createShimByName(PRE_2_7_SHIM_NAME);
-      } else {
-        SHIMS = createShimByName(CURRENT_SHIM_NAME);
+        LOG.warn("Hadoop " + VersionInfo.getVersion() + " support is dropped.");
       }
+      SHIMS = createShimByName(CURRENT_SHIM_NAME);
     }
     return SHIMS;
   }