Remove exceptions from birdsongrec.py

This removes NotADirectory and FileNotFound errors raised by
`birdsongrec2annot` when `wavpath` doesn't exist or it can't find
the wav files in the specified `wavpath`, respectively.

My intent was to make sure the files were there,
if something else depended on them.
But this prevents someone from accessing the annotations
if they don't have the wav files.
Which is the opposite of the point of this package.

src/crowsetta/birdsongrec.py

@@ -69,12 +69,6 @@ def birdsongrec2annot(annot_path='Annotation.xml', concat_seqs_into_songs=True,
     else:
         wavpath = Path(wavpath)
 
-    if not wavpath.exists():
-        raise NotADirectoryError(
-            "Value specified for 'wavpath' not recognized as an existing directory."
-            f"\nValue for 'wavpath' was: {wavpath}"
-        )
-
     # `birdsong-recongition-dataset` also has a 'Sequence' class
     # but it is slightly different from the `generic.Sequence` used by `crowsetta`
     seq_list_xml = birdsongrec.parse_xml(annot_path,
@@ -88,11 +82,7 @@ def birdsongrec2annot(annot_path='Annotation.xml', concat_seqs_into_songs=True,
 
         wav_filename = os.path.join(wavpath, seq_xml.wav_file)
         wav_filename = os.path.abspath(wav_filename)
-        if not os.path.isfile(wav_filename):
-            raise FileNotFoundError(
-                f'.wav file {wav_filename} specified in '
-                f'annotation file {annot_path} is not found'
-            )
+
         samp_freq = soundfile.info(wav_filename).samplerate
         onsets_s = np.round(onset_inds / samp_freq, decimals=3)
         offsets_s = np.round(offset_inds / samp_freq, decimals=3)