Remove escaping func for TXT content to fix constant update of TXT records

[Archirk]

Escaping semicolumn function, apparently redundant and causes always update of TXT records.
We can not provide unescaped ";" since errors is risen from this validation process:
https://github.com/octodns/octodns/blob/main/octodns/record/chunked.py#L53
So removed func always adds extra slash, which forces octodns during sync to think that updated is required.
e.g.
We have record described as:

some-txt:
  ttl: 120
  type: TXT
  value: v=DKIM1\; k=rsa\; p=MIG

Which during sync will say:

* selectel (SelectelProvider)
*   Create <TxtRecord TXT 120, some-txt.octodns-chirkov.com., ['v=DKIM1\; k=rsa\; p=MIG']> (config)
*   Summary: Creates=1, Updates=0, Deletes=0, Existing Records=0

But if do sync again:

* selectel (SelectelProvider)
*   Update
*     <TxtRecord TXT 120, some-txt.octodns-chirkov.com., ['v=DKIM1\\; k=rsa\\; p=MIG']> ->
*     <TxtRecord TXT 120, some-txt.octodns-chirkov.com., ['v=DKIM1\; k=rsa\; p=MIG']> (config)
*   Summary: Creates=0, Updates=1, Deletes=0, Existing Records=1

While on the server side result will remain the same v=DKIM1\; k=rsa\; p=MIG

[ross]

I don't have access to selectel so going to have to trust that this makes sense. Code-wise it's 👍