String dtype: remove fallback Perfomance warnings for string methods
Closes #58581

The current PR simply removes the warning altogether, but now we have the `"mode.performance_warnings"` option, we could in theory also keep the warnings as long as they are not enabled by default. 
However, the performance warnings option right now is still on by default. So if we want to do this right now (keep the string fallback warnings but not enabled by default), we would need to change that default to something like `None` which then means True/False depending on the case .. (cc @rhshadrach)


xref https://github.com/pandas-dev/pandas/issues/54792
My preference would be a simple Boolean show all vs show none (ref: https://github.com/pandas-dev/pandas/issues/55385#issue-1924986475). In any case, showing warnings when the user has no viable path of better performance doesn't seem appropriate. This looks good to me. OK, sounds good, let's then simply remove those for now.