Referenco to Znode in warning on dumpprivkey command

[Petr Vacha]

Describe the issue

When running dumpprivkey ADDRESS in Firo QT console warning text includes: "...it is not needed for Znode setup or diagnosis"

As Znodes are called just Masternodes, it should be instead:
"...it is not needed for Masternode setup or diagnosis" or "...it is not needed for Firo Masternode setup or diagnosis"

Local setup

MacOS, Firo Core version v0.14.12.1-gc7e3ef0e6 (64-bit)

[justanwar]

We wanted to do it fully which includes both cosmetic (such as this) and the underlying parts such as znodeblsprivkey in firo.conf and the evoznode commands, but would have meant slowing down other major features such as Spark.

Re: #959