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/01.GETTING-STARTED.md

@@ -53,20 +53,20 @@ python tools/build.py --profile=es5.1|es2015-subset|minimal
 
 See also the related [README.md](https://github.com/jerryscript-project/jerryscript/blob/master/jerry-core/profiles/README.md).
 
-**Use (jerry, compiler-default, external) libc**
+**Use (compiler-default, external) libc**
 
-The default libc is jerry-libc, but you can use compiler-default libc or an external libc:
+The default libc is the compiler-default libc but you can use an external libc as well:
 
 - compiler-default libc:
 
 ```bash
-python tools/build.py --jerry-libc=off
+python tools/build.py
 ```
 
 - external libc:
 
 ```bash
-python tools/build.py --jerry-libc=off --compile-flag="-nostdlib -I/path/to/ext-libc/include" --link-lib="ext-c"
+python tools/build.py --compile-flag="-nostdlib -I/path/to/ext-libc/include" --link-lib="ext-c"
 ```
 
 **Add toolchain file**
@@ -86,7 +86,7 @@ python tools/build.py --toolchain=cmake/toolchain_linux_armv7l.cmake
 **Use system memory allocator**
 
 ```bash
-python tools/build.py --system-allocator=on --jerry-libc=off
+python tools/build.py --system-allocator=on
 ```
 
 *Note*: System allocator is only supported on 32 bit systems.

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.