doc: Remove ParseInt mentions in documentation

In the dev notes, remove the whole section, because:

* ParseDouble was removed in commit
  fa9d72a794
* The locale-dependent atoi is already checked by
  test/lint/lint-locale-dependence.py

Co-authored-by: Fabian Jahr <fjahr@protonmail.com>

doc/developer-notes.md

@@ -1009,10 +1009,6 @@ Strings and formatting
     buffer overflows, and surprises with `\0` characters. Also, some C string manipulations
     tend to act differently depending on platform, or even the user locale.
 
-- Use `ToIntegral` from [`strencodings.h`](/src/util/strencodings.h) for number parsing. In legacy code you might also find `ParseInt*` family of functions, `ParseDouble` or `LocaleIndependentAtoi`.
-
-  - *Rationale*: These functions do overflow checking and avoid pesky locale issues.
-
 - For `strprintf`, `LogInfo`, `LogDebug`, etc formatting characters don't need size specifiers.
 
   - *Rationale*: Bitcoin Core uses tinyformat, which is type safe. Leave them out to avoid confusion.