bug#39789: eieio Info misspells slot name in eieio-instance-tracker

[akater]

I'm using Emacs 28 from git master.

Excerpt from EIEIO entry in Info Directory:
> Sometimes it is useful to keep a master list of all instances of a
> given class.  The class ‘eieio-instance-tracker’ performs this task.

>  -- Class: eieio-instance-tracker tracker-symbol
>      Enable instance tracking for this class.  The slot TRACKER-SYMBOL
>      should be initialized in inheritors of this class to a symbol
>      created with ‘defvar’.  This symbol will serve as the variable used
>      as a master list of all objects of the given class.

At the moment, eieio-instance-tracker is defined in eieio-base with slot
named

> TRACKING-SYMBOL

not

> TRACKER-SYMBOL

EIEIO entry in Info Directory should thus be patched to refer to slot's
actual name `tracking-symbol'. These are the only two mentions of the
slot in eieio.info.bz2