Fixing typo in db.Config.MaxLifetime default and removing unused db.DefaultPlanCacheDisabled.

[dhermes]

PR Summary

• Type: Bugfix
• Intended Change Level: patch

Reviewers:

Reviewers keep the following in mind while reviewing this PR, and provide an assessment of them in your approval comment:

• Does the "Intended Change Level" above match the actual behavior of this PR?
• Is this PR following patterns set forth in the package (if modifying a package), or the go-sdk design patterns if implementing a new package from scratch?
• Does this require a backport to LTS versions? If so ping, let the contributors group know.

[codecov]

Codecov Report

Merging #222 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #222      +/-   ##
==========================================
+ Coverage   67.54%   67.55%   +0.01%     
==========================================
  Files         563      563              
  Lines       30436    30438       +2     
==========================================
+ Hits        20557    20562       +5     
+ Misses       8604     8601       -3     
  Partials     1275     1275              

Impacted Files	Coverage Δ
db/config.go	89.13% <100.00%> (+0.11%)	⬆️
logger/worker.go	67.44% <0.00%> (+3.48%)	⬆️

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[wcharczuk]

LGTM