[MINOR][SQL] Remove unused TableSchema constructor

[the-sakthi]

What changes were proposed in this pull request?

This PR removes the unused TableSchema(int numColumns) constructor, which was previously marked with a TODO comment for removal.

Why are the changes needed?

The constructor is no longer required and does not serve any functional purpose in the codebase. Eliminating this dead code enhances code maintainability and readability.

Does this PR introduce any user-facing change?

No

How was this patch tested?

Existing tests and moreover we don't use this constructor anywhere in the codebase:

❯ git grep "new TableSchema"
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetCatalogsOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetColumnsOperation.java:  protected static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetColumnsOperation.java:          TableSchema schema = new TableSchema(metastoreClient.getSchema(dbName,
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetCrossReferenceOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetFunctionsOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetPrimaryKeysOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetSchemasOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetTableTypesOperation.java:  protected static TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetTablesOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/GetTypeInfoOperation.java:  private static final TableSchema RESULT_SET_SCHEMA = new TableSchema()
sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/operation/OperationManager.java:    TableSchema tableSchema = new TableSchema(getLogSchema());

Was this patch authored or co-authored using generative AI tooling?

No

[LuciferYang]

This part of the code originates from Hive. Please do not modify it unless absolutely necessary. However, if there is a corresponding patch in Hive to remove it, may port it over and provide supplementary descriptions in the pull request (PR).

[the-sakthi]

Thanks for the review @LuciferYang ! Will check and do the needful.