remove support for non jl file support

[aviatesk]

xref: timholy/Revise.jl#921

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.60%. Comparing base (923fe46) to head (7b39dbc).
Report is 22 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (923fe46) and HEAD (7b39dbc). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (923fe46)	HEAD (7b39dbc)
	10	8

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #141       +/-   ##
===========================================
- Coverage   89.50%   69.60%   -19.90%     
===========================================
  Files           3        3               
  Lines         381      408       +27     
===========================================
- Hits          341      284       -57     
- Misses         40      124       +84     

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