feat(db): remove workaround for pqsql 9.4 and older

The workaround was required because "ON CONFLICT DO NOTHING" was added with pqsql 9.5.

PostgreSQL 9.4 is eol since 2020-02-13 and thus everyone should use a version with upsert support nowadays.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

lib/private/DB/AdapterPgSql.php

@@ -25,10 +25,6 @@ public function fixupStatement($statement) {
 	}
 
 	public function insertIgnoreConflict(string $table, array $values) : int {
-		if ($this->isPre9_5CompatMode() === true) {
-			return parent::insertIgnoreConflict($table, $values);
-		}
-
 		// "upsert" is only available since PgSQL 9.5, but the generic way
 		// would leave error logs in the DB.
 		$builder = $this->conn->getQueryBuilder();
@@ -39,17 +35,4 @@ public function insertIgnoreConflict(string $table, array $values) : int {
 		$queryString = $builder->getSQL() . ' ON CONFLICT DO NOTHING';
 		return $this->conn->executeUpdate($queryString, $builder->getParameters(), $builder->getParameterTypes());
 	}
-
-	protected function isPre9_5CompatMode(): bool {
-		if ($this->compatModePre9_5 !== null) {
-			return $this->compatModePre9_5;
-		}
-
-		$result = $this->conn->executeQuery('SHOW SERVER_VERSION');
-		$version = $result->fetchOne();
-		$result->free();
-		$this->compatModePre9_5 = version_compare($version, '9.5', '<');
-
-		return $this->compatModePre9_5;
-	}
 }