Remove pmd.xml

[chingor13]

We are using google-java-format for code formatting/linting.

Fixes#4751

[codecov]

Codecov Report

Merging #5790 into master will decrease coverage by 1.07%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #5790 +/- ##
============================================
- Coverage 47.17% 46.1% -1.08% + Complexity 25130 24189 -941 
============================================
Files 2389 2456 +67 Lines 259836 262158 +2322 Branches 29417 29602 +185 ============================================
- Hits 122585 120875 -1710 - Misses 128321 132172 +3851 - Partials 8930 9111 +181

Impacted Files	Coverage Δ	Complexity Δ
.../java/com/google/cloud/testing/CommandWrapper.java	90.9% <0%> (-6.07%)	13% <0%> (ø)
...in/java/com/google/cloud/storage/StorageBatch.java	88% <0%> (-4%)	13% <0%> (ø)
...m/google/cloud/vision/v1/ImageAnnotatorClient.java	58.69% <0%> (-3.31%)	15% <0%> (-4%)
...e/cloud/vision/v1p4beta1/ImageAnnotatorClient.java	58.69% <0%> (-3.31%)	15% <0%> (-4%)
...gle/cloud/storage/testing/RemoteStorageHelper.java	61.98% <0%> (-3.06%)	9% <0%> (ø)
...e/cloud/vision/v1p3beta1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
...e/cloud/vision/v1p2beta1/ImageAnnotatorClient.java	47.05% <0%> (-2.95%)	9% <0%> (-2%)
.../java/com/google/cloud/speech/v1/SpeechClient.java	48.57% <0%> (-2.78%)	10% <0%> (-2%)
...om/google/cloud/speech/v1p1beta1/SpeechClient.java	48.57% <0%> (-2.78%)	10% <0%> (-2%)
...d/webrisk/v1beta1/WebRiskServiceV1Beta1Client.java	63.41% <0%> (-2.5%)	12% <0%> (-3%)
... and 853 more

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