ide-tape remove pipeline speed/control calculations

Pipeline handling calculations in idetape_calculate_speeds() can
go since they do not have any effect on other functionality besides:

1. info is only being exported through /proc as a read-only item
(controlled_pipeline_head_speed, uncontrolled_pipeline_head_speed)

2. used in idetape_restart_speed_control() which, in turn, is unrelated to
other code

3. used only for pipeline frames number accounting (tape->pipeline_head),
also unused elsewhere.

4.some variables are:
        only written to: tape->buffer_head;
        unused: tape->tape_head, tape->last_tape_head

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>