Remove the idle process.

Remove the idle process.

We can get rid of the idle process also with the preemptive kernel and
perform the idle loop inside proc_schedule().

In this way we can reduce the kernel memory footprint and better
optimize memory usage.

== avr-kern example ==
<before>
   text    data     bss     dec     hex filename
  24632     238    5713   30583    7777 images/avr-kern.elf
<after>
   text    data     bss     dec     hex filename
  24498     234    5521   30253    762d images/avr-kern.elf

== at91sam7x example ==
<before>
   text    data     bss     dec     hex filename
  42416     184   10120   52720    cdf0 images/at91sam7x.elf
<after>
   text    data     bss     dec     hex filename
  42228     184    9748   52160    cbc0 images/at91sam7x.elf

git-svn-id: https://src.develer.com/svnoss/bertos/trunk@3250 38d2e660-2303-0410-9eaa-f027e97ec537