code: def dropAssayFromStudy(assayNum, studyNum, pathToISATABFile):
      
      from isatools import isatab
      import os
      try:
          isa = isatab.load(pathToISATABFile, skip_load_tables=True)
          std = isa.studies[studyNum - 1]
          assays = std.assays
          if os.path.isfile(os.path.join(pathToISATABFile,assays[assayNum - 1].filename)):
              os.remove(os.path.join(pathToISATABFile,assays[assayNum - 1].filename))
          del assays[assayNum - 1]
          isatab.dump(isa_obj=isa, output_path=pathToISATABFile)
      except FileNotFoundError as err:
          raise err
docs: This function removes an Assay from a study in an ISA file
      Typically, you should use the exploreISA function to check the contents
      of the ISA file and retrieve the assay and study numbers you are interested in!
      :param assayNum: The Assay number (notice it's 1-based index).
      :type assayNum: int
      :param studyNum: The Study number (notice it's 1-based index).
      :type studyNum: int
      :param pathToISATABFile: The path to the ISATAB file
      :type pathToISATABFile: string
      :raise FileNotFoundError: If pathToISATABFile does not contain file 'i_Investigation.txt'.