Fix leftover deprecated nosetest teardown methods

[djhoese]

I/we must have switched setup to setup_method in some tests that were using the deprecated nose-style setup methods, but forgot to change the teardown methods too.

• Closes #xxxx
• Tests added
• Fully documented

[codecov]

Codecov Report

Merging #2486 (89dba92) into main (142dc57) will increase coverage by 0.00%.
The diff coverage is 86.66%.

@@           Coverage Diff           @@
##             main    #2486   +/-   ##
=======================================
  Coverage   94.83%   94.83%           
=======================================
  Files         337      337           
  Lines       49421    49426    +5     
=======================================
+ Hits        46866    46871    +5     
  Misses       2555     2555           

Flag	Coverage Δ
behaviourtests	4.42% <0.00%> (-0.01%)	⬇️
unittests	95.45% <86.66%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/tests/test_readers.py	98.90% <83.33%> (+0.01%)	⬆️
satpy/tests/reader_tests/test_fy4_base.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_ghi_l1.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_msu_gsa_l1b.py	100.00% <100.00%> (ø)

[coveralls]

Pull Request Test Coverage Report for Build 5004366325

• 13 of 15 (86.67%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.0005%) to 95.399%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
satpy/tests/test_readers.py	10	12	83.33%

Totals
Change from base Build 4995535188:	0.0005%
Covered Lines:	46984
Relevant Lines:	49250

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💛 - Coveralls