Remove jerry-libc (#2332)

Rationale:
- There is no port under targets/ that would use it. All of them
  turn it off when building.
- That's no surprise, as jerry-libc supports no barebone MCUs but
  posix targets with syscalls only. Actually, that's Linux only,
  because macOS builds have turned off the use of jerry-libc a
  while ago.
- And there is no point in maintaining a highly restricted set of
  libc functions: as soon as someone wants to use JerryScript in a
  scenario that needs more functions than jerry-main, they have to
  choose a different libc (most problably the compiler's default
  one).

I think that we should not keep supporting an otherwise unused
library for the purposes of jerry-main on arm/x86/x64-linux  only.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

tools/check-sonarqube.sh

@@ -23,7 +23,6 @@ then
     ./tools/build.py --error-messages=on \
                      --jerry-cmdline-snapshot=on \
                      --jerry-debugger=on \
-                     --jerry-libc=off \
                      --line-info=on \
                      --mem-stats=on \
                      --profile=es2015-subset \
@@ -38,7 +37,6 @@ else
   ./tools/build.py --error-messages=on \
                    --jerry-cmdline-snapshot=on \
                    --jerry-debugger=on \
-                   --jerry-libc=off \
                    --line-info=on \
                    --mem-stats=on \
                    --profile=es2015-subset \