eshell-previous-prompt broken on Emacs 30

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- [X] I have read "[How to Debug Issues](https://doomemacs.org/d/how2debug)", and will use it to provide as much information about this issue as possible.

- [X] The issue can be reproduced on the **latest** available commit of Doom.

- [X] The issue can be reproduced on a stable release of Emacs, such as 27 or 28. *(Doom does not support development builds like 29+ or any version ending in .50 or .9x)*

### Expected behavior

In Emacs 30, `eshell-prompt-regexp` has been declared obsolete and searching for prompts is done using text properties now, as below
The issue is that now `eshell-previous-prompt` is broken because of the newline character `+eshell-default-prompt-fn` inserts in the beginning. I propose removing the `(if (bobp) "" "\n")` from the Eshell prompt function.

### System Information

https://pastebin.com/3EgWg6NR