runtimevar/awsparamstore: drop the DescribeParameters call, it isn't necessary

[vangent]

Fixes #3134.

[codecov]

Codecov Report

Merging #3146 (60ba690) into master (e0f202b) will decrease coverage by 0.02%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #3146      +/-   ##
==========================================
- Coverage   72.44%   72.42%   -0.03%     
==========================================
  Files         112      112              
  Lines       14329    14273      -56     
==========================================
- Hits        10381    10337      -44     
+ Misses       3231     3226       -5     
+ Partials      717      710       -7     

Impacted Files	Coverage Δ
runtimevar/awsparamstore/awsparamstore.go	88.41% <81.81%> (+2.50%)	⬆️

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