database/sql: Remove unnecessary call to maybeOpenNewConnections

numCanOpen will never be larger than 0 in maybeOpenNewConnections() when this
code path is taken, so no new connections can ever be opened.

Change-Id: Id1302e8d9afb3a67be61b5e738fe07ef81d20fe0
Reviewed-on: https://go-review.googlesource.com/1550Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/database/sql/sql.go

@@ -644,7 +644,6 @@ func (db *DB) conn() (*driverConn, error) {
 		// connectionOpener doesn't block while waiting for the req to be read.
 		req := make(chan connRequest, 1)
 		db.connRequests = append(db.connRequests, req)
-		db.maybeOpenNewConnections()
 		db.mu.Unlock()
 		ret := <-req
 		return ret.conn, ret.err