Remove Conn.lastActivityTime

It was only read in one place and that was an optimization to get the
current time. Replaced that usage with time.Now()

conn.go

@@ -111,8 +111,7 @@ func (cc *ConnConfig) networkAddress() (network, address string) {
 // Use ConnPool to manage access to multiple database connections from multiple
 // goroutines.
 type Conn struct {
-	conn               net.Conn  // the underlying TCP or unix domain socket connection
-	lastActivityTime   time.Time // the last time the connection was used
+	conn               net.Conn // the underlying TCP or unix domain socket connection
 	wbuf               []byte
 	pid                uint32            // backend pid
 	secretKey          uint32            // key to use to send a cancel query message to the server
@@ -307,7 +306,6 @@ func (c *Conn) connect(config ConnConfig, network, address string, tlsConfig *tl
 	c.RuntimeParams = make(map[string]string)
 	c.preparedStatements = make(map[string]*PreparedStatement)
 	c.channels = make(map[string]struct{})
-	c.lastActivityTime = time.Now()
 	c.cancelQueryCompleted = make(chan struct{})
 	close(c.cancelQueryCompleted)
 	c.doneChan = make(chan struct{})
@@ -1423,8 +1421,6 @@ func (c *Conn) rxMsg() (pgproto3.BackendMessage, error) {
 		return nil, err
 	}
 
-	c.lastActivityTime = time.Now()
-
 	// fmt.Printf("rxMsg: %#v\n", msg)
 
 	return msg, nil
@@ -1742,7 +1738,6 @@ func (c *Conn) ExecEx(ctx context.Context, sql string, options *QueryExOptions,
 	defer c.unlock()
 
 	startTime := time.Now()
-	c.lastActivityTime = startTime
 
 	commandTag, err := c.execEx(ctx, sql, options, arguments...)
 	if err != nil {

query.go

@@ -342,7 +342,7 @@ func (c *Conn) getRows(sql string, args []interface{}) *Rows {
 	c.preallocatedRows = c.preallocatedRows[0 : len(c.preallocatedRows)-1]
 
 	r.conn = c
-	r.startTime = c.lastActivityTime
+	r.startTime = time.Now()
 	r.sql = sql
 	r.args = args
 
@@ -368,7 +368,6 @@ type QueryExOptions struct {
 }
 
 func (c *Conn) QueryEx(ctx context.Context, sql string, options *QueryExOptions, args ...interface{}) (rows *Rows, err error) {
-	c.lastActivityTime = time.Now()
 	rows = c.getRows(sql, args)
 
 	err = c.waitForPreviousCancelQuery(ctx)

replication.go

@@ -330,8 +330,6 @@ func (rc *ReplicationConn) WaitForReplicationMessage(ctx context.Context) (*Repl
 }
 
 func (rc *ReplicationConn) sendReplicationModeQuery(sql string) (*Rows, error) {
-	rc.c.lastActivityTime = time.Now()
-
 	rows := rc.c.getRows(sql, nil)
 
 	if err := rc.c.lock(); err != nil {