Remove redundant checks after memory allocations

:Release Notes:
Avoid useless checks after g_new(), g_strdup() to simplify the code.

:Detailed Notes:
Glib promises to terminate the process when not enough memory for
g_malloc(), g_new(), g_strdup() and similar. So there's no point in
checking what these functions return.

:Testing Performed:
Unit tests under valgrind.
Tested on device and in emulator.

:QA Notes:

:Issues Addressed:
[GF-43049] pbnjson: Remove redundant checks after memory allocations

Open-webOS-DCO-1.0-Signed-off-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>

Change-Id: I34f9f9fe6473ad9a577727baf7343320d8d81018
Reviewed-on: https://g2g.palm.com/3701
Reviewed-by: Build Verification
Reviewed-by: Mykola Kryvonos <mykola.kryvonos@lge.com>
Tested-by: Mykola Kryvonos <mykola.kryvonos@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Tested-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Reviewed-by: Keith Derrick <keith.derrick@lge.com>