toolchain-external: remove experimental Blackfin toolchain

The 2014R1 toolchain is provided in two flavours by Analog Devices:
one based on gcc 4.3.x, which is considered stable, and one based on
gcc 4.5.x, considered experimental. In commit
5a65b8e1 ("toolchain-external: add ADI
Blackfin 2014R1 toolchain, remove 2012R1") both variants were added.

However, after some testing in the autobuilders, and discussion with
the Analog Devices folks, it turns out that the experimental version
of the toolchain is too experimental. It causes numerous build
failures, and the Analog Devices folks clearly say that it's an early
release and that they expect quite a few problems to show up.

Therefore, this commit removes the experimental flavor and keeps only
the stable variant. Note that the removal/renaming of the Config.in
options is not a problem, since those options were added after the
2014.05 release.

Fixes:

  http://autobuild.buildroot.org/results/2a9/2a9d9c332a206fdb46bc8ba022c74d23082a6312/
  http://autobuild.buildroot.org/results/e1c/e1ce0c1cdd0139208dddaa8f2441ab0e3ab2385e/
  http://autobuild.buildroot.org/results/993/993aca3f4719afaa4b37524f9136fb8cdc53a066/


  and more.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>