es519xx: fix continuity mode handling

Depending on the chip, the limit value for the buzzer is between 25 and 35 Ω,
so this code set the limit for continuity to 25 Ω to be on the safe side.
es519xx: correctly handle the voltage factor in diode mode
es519xx: fix switching between frequency and duty cycle mode on 14 bytes chips

Here is what the datasheet says about this:
  "If judge bit is 1, it means frequency mode. If judge bit is 0,
   it means duty cycle mode."
But this is plain wrong. Reality proves this is the other way around.
es519xx: apply the proper fixed factor in duty cycle mode
es519xx: correctly handle the VAHZ function

This handles the frequency and duty cycle display in voltage or current mode.
switch the UNI-T UT61E driver to the new es519xx parser
remove the es51922 protocol parser, superseded by the es519xx protocol parser