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

docs/07.DEBUGGER.md

@@ -13,13 +13,11 @@ development environments.
 
 The following arguments must be passed to `tools/build.py`:
 
-`--jerry-debugger=on --jerry-libc=off`
+`--jerry-debugger=on`
 
 The transport layer of the communication protocol is pluggable.
 At the moment, a WebSocket-based implementation is provided as a
 JerryScript extension, which transmits messages over TCP/IP networks.
-This implementation requires a socket API which is not yet
-supported by jerry-libc so the standard libc is used instead.
 If necessary/implemented, any reliable stream or datagram based
 protocol can be used for transmitting debugger messages.