PostgreSQL: Remove feature toggle postgresDSUsePGX (#113675)

* PostgreSQL: Remove feature toggle `postgresDSUsePGX`

* Fix tests and linting

* Address review comments

pkg/tsdb/grafana-postgresql-datasource/postgres_snapshot_test.go

@@ -1,7 +1,6 @@
 package postgres
 
 import (
-	"context"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -23,7 +22,7 @@ import (
 var updateGoldenFiles = false
 
 // These tests require a real postgres database:
-// - make devenv sources=potgres_tests
+// - make devenv sources=postgres_tests
 // - either set the env variable GRAFANA_TEST_DB = postgres
 //   - or set `forceRun := true` below
 //
@@ -127,6 +126,8 @@ func TestIntegrationPostgresSnapshots(t *testing.T) {
 		{format: "table", name: "types_char"},
 		{format: "table", name: "types_datetime"},
 		{format: "table", name: "types_other"},
+		{format: "table", name: "types_enum"},
+		{format: "table", name: "types_jsonb"},
 		{format: "table", name: "timestamp_convert_bigint"},
 		{format: "table", name: "timestamp_convert_integer"},
 		{format: "table", name: "timestamp_convert_real"},
@@ -148,10 +149,11 @@ func TestIntegrationPostgresSnapshots(t *testing.T) {
 			}
 
 			jsonData := sqleng.JsonData{
-				MaxOpenConns:        0,
+				MaxOpenConns:        10,
 				MaxIdleConns:        2,
 				ConnMaxLifetime:     14400,
 				Timescaledb:         false,
+				Mode:                "disable",
 				ConfigurationMethod: "file-path",
 			}
 
@@ -164,28 +166,24 @@ func TestIntegrationPostgresSnapshots(t *testing.T) {
 
 			cnnstr := getCnnStr()
 
-			db, handler, err := newPostgres(context.Background(), "error", 10000, dsInfo, cnnstr, logger, backend.DataSourceInstanceSettings{})
-
-			t.Cleanup((func() {
-				_, err := db.Exec("DROP TABLE tbl")
-				require.NoError(t, err)
-				err = db.Close()
-				require.NoError(t, err)
-			}))
-
+			p, handler, err := newPostgres(t.Context(), "error", 10000, dsInfo, cnnstr, logger, backend.DataSourceInstanceSettings{})
 			require.NoError(t, err)
 
+			t.Cleanup(func() {
+				p.Close()
+			})
+
 			sqlFilePath := filepath.Join("testdata", test.format, test.name+".sql")
 			goldenFileName := filepath.Join(test.format, test.name+".golden")
 
 			rawSQL, sql := readSqlFile(sqlFilePath)
 
-			_, err = db.Exec(sql)
+			_, err = p.Exec(t.Context(), sql)
 			require.NoError(t, err)
 
 			query := makeQuery(rawSQL, test.format)
 
-			result, err := handler.QueryData(context.Background(), &query)
+			result, err := handler.QueryData(t.Context(), &query)
 			require.Len(t, result.Responses, 1)
 			response, found := result.Responses["A"]
 			require.True(t, found)