Removed if (plottype not in _valid_types_all) ...

This is unnecessary because the kwarg validator already check whether `kwarg['type']` is in `_valid_types_all`. So if the value passed the validator then it must be in `_valid_types_all`. So we don't need to check again in function `_get_valid_plot_types` (unless...this function is used also by function other than `plotting.plot`)

Author: anbarief

src/mplfinance/_arg_validators.py

@@ -93,13 +93,9 @@ def _get_valid_plot_types(plottype=None):
 
     if plottype is None:
         return _valid_types_all
-
-    if plottype not in _valid_types_all:
-        return None
     elif plottype in _alias_types:
         return _alias_types[plottype]
-    else:
-        return plottype
+    return plottype
 
 
 def _mav_validator(mav_value):