Clean-up pom.xml to remove plugin warnings; resolves #273.

[ruebot]

GitHub issue(s): #273

What does this Pull Request do?

• Clean-up pom.xml to remove plugin warnings; resolves Maven build warning during release #273.
• The removed javadoc.plugin.version is because there were actually two of them in that section with two different versions. 🤯

How should this be tested?

• TravisCI should pass.
• Local build should not show previous warnings (as shown in Maven build warning during release #273) during this build or
  • mvn release:clean
  • mvn release:prepare -DreleaseVersion=0.17.1 -DdevelopmentVersion=0.17.2-SNAPSHOT -DautoVersionSubmodules=true -DpushChanges=false

Additional Notes:

Not sure how to have others test this since you might need signing keys setup, and a ~/.m2/settings.xml setup as described here

[codecov-io]

Codecov Report

Merging #274 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #274   +/-   ##
=======================================
  Coverage   70.36%   70.36%           
=======================================
  Files          41       41           
  Lines        1046     1046           
  Branches      192      192           
=======================================
  Hits          736      736           
  Misses        244      244           
  Partials       66       66

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[ianmilligan1]

Tested using mvn release:clean and mvn release:prepare -DreleaseVersion=0.17.1 -DdevelopmentVersion=0.17.2-SNAPSHOT -DautoVersionSubmodules=true -DpushChanges=false, builds fine w/o the error messages as noted in #273.

[lintool]

lgtm