Deprecate *getunitname script command

[AnnieRuru]

After I give it some thought, I think better split the *getunitname deprecation out from #2391

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Pull Request Prelude

• I have followed proper Hercules code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR will be closed if the above-mentioned criteria are not fulfilled.

Issues addressed

we have 2 script command do the same thing, *rid2name and *getunitname

Changes Proposed

deprecate *getunitname because rid2name has been exist since eathena times
also minor fix rid2name to support elementals

Affected Branches

• Master

Known Issues and TODO List

we have to decide which one to deprecate,
better don't have 2 script commands do exact same thing again, like this #2089

[HerculesWSAPI]

This change is 

[bWolfie]

getunit... commands would be more consistent in documentation, as there are many commands of that name and they can be grouped together.

Plus we already set the precedent by deprecating *specialeffect2() which was used in many official scripts. Not exactly the same situation, but similar.

[Asheraf]

I don't feel deprecating getunitname() is a good idea, It's more popular than rid2name() and consistent with the other data retrieval commands.

[AnnieRuru]

..... I was lost in making getmercinfo/getpetinfo/gethominfo/geteleminfo,

actually I want to keep both

getunitname will be real time name, and rid2name will be database name

example 1.
if player having @fakename,
getunitname will display fakename
rid2name will display real character name

example 2
monster("this", -1,-1,"BOSSS",PORING,1)
getunitname will display BOSSS
rid2name will display Poring

I read through the source code and found getunitname call the function status_get_name,
which was use in clif ..... to display in client-side

.... another thing worth mention
DO NOT use getnameditem Knife, getunitname(getcharid(CHAR_ID_ACCOUNT));
because if the player under @fakename,
*getunitname script command will return fakename of the character
has to use rid2name

..... ok go back complete my getpetinfo script command ....
scrap this one, redo the above
https://github.com/AnnieRuru/customs/blob/master/plugin/rid2name.diff