deprecate process_synthetic_data in favour of process_mth5

[codecov[bot]]

Codecov Report

Merging #272 (a54faad) into fourier_coefficients (8cf0fdd) will decrease coverage by 0.03%. The diff coverage is 100.00%.

@@                   Coverage Diff                    @@
##           fourier_coefficients     #272      +/-   ##
========================================================
- Coverage                 77.52%   77.49%   -0.03%     
========================================================
  Files                        84       84              
  Lines                      5147     5123      -24     
========================================================
- Hits                       3990     3970      -20     
+ Misses                     1157     1153       -4     

Impacted Files	Coverage Δ
aurora/pipelines/process_mth5.py	98.18% <ø> (ø)
aurora/test_utils/synthetic/processing_helpers.py	100.00% <ø> (+14.28%)	:arrow_up:
tests/io/test_issue_139.py	93.47% <ø> (-0.76%)	:arrow_down:
tests/parkfield/test_process_parkfield_run.py	93.47% <100.00%> (-0.40%)	:arrow_down:
.../synthetic/test_compare_aurora_vs_archived_emtf.py	97.50% <100.00%> (ø)
tests/synthetic/test_processing.py	94.16% <100.00%> (ø)