[SPARK-19961][SQL][MINOR] unify a erro msg when drop databse for...

[SPARK-19961][SQL][MINOR] unify a erro msg when drop databse for HiveExternalCatalog and InMemoryCatalog

## What changes were proposed in this pull request?

unify a exception erro msg for dropdatabase when the database still have some tables for HiveExternalCatalog and InMemoryCatalog
## How was this patch tested?
N/A

Author: windpiger <songjun@outlook.com>

Closes #17305 from windpiger/unifyErromsg.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/InMemoryCatalog.scala

@@ -127,7 +127,7 @@ class InMemoryCatalog(
       if (!cascade) {
         // If cascade is false, make sure the database is empty.
         if (catalog(db).tables.nonEmpty) {
-          throw new AnalysisException(s"Database '$db' is not empty. One or more tables exist.")
+          throw new AnalysisException(s"Database $db is not empty. One or more tables exist.")
         }
         if (catalog(db).functions.nonEmpty) {
           throw new AnalysisException(s"Database '$db' is not empty. One or more functions exist.")

sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLSuite.scala

@@ -617,12 +617,8 @@ abstract class DDLSuite extends QueryTest with SQLTestUtils {
     val message = intercept[AnalysisException] {
       sql(s"DROP DATABASE $dbName RESTRICT")
     }.getMessage
-    // TODO: Unify the exception.
-    if (isUsingHiveMetastore) {
-      assert(message.contains(s"Database $dbName is not empty. One or more tables exist"))
-    } else {
-      assert(message.contains(s"Database '$dbName' is not empty. One or more tables exist"))
-    }
+    assert(message.contains(s"Database $dbName is not empty. One or more tables exist"))
+
 
     catalog.dropTable(tableIdent1, ignoreIfNotExists = false, purge = false)