Fix extension samples

[bryates]

We should not have any -ext files in our repo. The idea behind extensions is they are summed together with the main sample, so the sum of weights contains all events. The make_jsons.py script looks for _ext

topeft/analysis/topeft_run2/make_jsons.py

Line 1673 in ec0ad94

if '_ext' in out_name:

so there must have been a mistake when these were entered as -ext.
Example:

topeft/input_samples/cfgs/2022_mc_background_samples.cfg

Line 25 in ec0ad94

../../input_samples/sample_jsons/background_samples/central_2022/ST_tW_Semileptonic-ext1.json