[!!!][TASK] Remove deprecated code from charset converter

The CharsetConverter class can now be reduced into smaller parts due
to deprecation removals.

Properties now marked as internal:
- parsedCharsets
- noCharByteVal
- toASCII
- twoByteSets
- eucBasedSets

Removed properties:
- synonyms

Removed public methods:
- parse_charset
- convArray
- utf8_to_entities
- entities_to_utf8
- crop
- convCaseFirst
- utf8_char2byte_pos

Removed arguments from public methods:
- 4th argument $useEntityForNoChar of conv

Resolves: #87194
Releases: master
Change-Id: I7ec967a076e9c43f62d95f1912574d3784b924d1
Reviewed-on: https://review.typo3.org/59190


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>