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-vera.sh

@@ -17,7 +17,6 @@
 JERRY_CORE_FILES=`find ./jerry-core -name "*.c" -or -name "*.h"`
 JERRY_EXT_FILES=`find ./jerry-ext -name "*.c" -or -name "*.h"`
 JERRY_PORT_FILES=`find ./jerry-port -name "*.c" -or -name "*.h"`
-JERRY_LIBC_FILES=`find ./jerry-libc -name "*.c" -or -name "*.h"`
 JERRY_LIBM_FILES=`find ./jerry-libm -name "*.c" -or -name "*.h"`
 JERRY_MAIN_FILES=`find ./jerry-main -name "*.c" -or -name "*.h"`
 UNIT_TEST_FILES=`find ./tests/unit-* -name "*.c" -or -name "*.h"`
@@ -29,4 +28,4 @@ fi
 
 vera++ -r tools/vera++ -p jerry \
  -e --no-duplicate \
- $MANUAL_CHECK_FILES $JERRY_CORE_FILES $JERRY_EXT_FILES $JERRY_PORT_FILES $JERRY_LIBC_FILES $JERRY_LIBM_FILES $JERRY_MAIN_FILES $UNIT_TEST_FILES
+ $MANUAL_CHECK_FILES $JERRY_CORE_FILES $JERRY_EXT_FILES $JERRY_PORT_FILES $JERRY_LIBM_FILES $JERRY_MAIN_FILES $UNIT_TEST_FILES