Refactor jrt buffer operations

`jrt_read_from_buffer_by_offset` is not used anywhere in the code
while `jrt_write_to_buffer_by_offset` is only used by snapshot
saving functions. Thus, this patch removes the read variant
completely and moves the write variant as a static function to
jerry.c. This empties out jrt.c, thus deleting.

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

jerry-core/jrt/jrt.h

@@ -160,7 +160,4 @@ extern void jerry_ref_unused_variables (void *, ...);
 #define JERRY_MIN(v1, v2) (((v1) < (v2)) ? (v1) : (v2))
 #define JERRY_MAX(v1, v2) (((v1) < (v2)) ? (v2) : (v1))
 
-extern bool jrt_read_from_buffer_by_offset (const uint8_t *, size_t, size_t *, void *, size_t);
-extern bool jrt_write_to_buffer_by_offset (uint8_t *, size_t, size_t *, const void *, size_t);
-
 #endif /* !JRT_H */