docs/manual: remove FAQ entry about 'depends on' vs. 'select'

The FAQ is before the section on package development, and only covers
user issues, not developer issues, so the FAQ entry about 'depends on'
vs. 'select' really doesn't have its place here.

And the 'depends on' vs. 'select' issue is already covered in a later
section, see
http://buildroot.org/downloads/manual/manual.html#depends-on-vs-select

.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>