revert check_ngsi2 function

[AlvaroVega]

Introduced by #947

All these CI test are failing:

>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_JSON and HTTP binding -- @1.1 2 min 17 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_JSON and HTTP binding -- @1.2 2 min 19 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_JSON and HTTP binding -- @1.3 2 min 21 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_JSON and HTTP binding -- @1.4 2 min 30 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_JSON and HTTP binding -- @1.1 2 min 27 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_JSON and HTTP binding -- @1.2 2 min 33 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_JSON and HTTP binding -- @1.3 2 min 17 sec 3
>>> features.TS02_iotaflows.004_iotajsonhttp2cb.IOT-iota004 IOTA_JSON with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_JSON and HTTP binding -- @1.4 2 min 52 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_UL and HTTP binding -- @1.1 2 min 34 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_UL and HTTP binding -- @1.2 2 min 12 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_UL and HTTP binding -- @1.3 2 min 23 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_1 Simple measure received thought IOTA_UL and HTTP binding -- @1.4 2 min 16 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_UL and HTTP binding -- @1.1 2 min 15 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_UL and HTTP binding -- @1.2 2 min 22 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_UL and HTTP binding -- @1.3 2 min 14 sec 3
>>> features.TS02_iotaflows.001_iotaulhttp2cb.IOT-iota001 IOTA_UL with HTTP binding to CB through IOTA.SC_2 Multiple measure received thought IOTA_UL and HTTP binding -- @1.4

iot-iota-ul                 | time=2020-12-04T09:53:11.185Z | lvl=FATAL | corr=n/a | trans=n/a | op=IoTAgentNGSI.Global | from=n/a | srv=n/a | subsrv=n/a | msg=An unexpected exception has been raised. Ignoring: TypeError: iotAgentLib.configModule.checkNgsi2 is not a function | comp=IoTAgent

Used by current iotas (ul, json...)
Backward compatibility is a must.

[fgalan]

LGTM