Remove Data from metric assertion class names

[anuraaga]

Trace assertions have some mix of Data or not on whether there is a corresponding SDK class for it, but this isn't really very helpful. An assertion is an assertion and there's not much need for the word - for metrics we can clean up a bit

[codecov]

Codecov Report

Merging #4433 (0c14d9e) into main (4a2814b) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #4433      +/-   ##
============================================
+ Coverage     90.00%   90.05%   +0.05%     
- Complexity     4885     4927      +42     
============================================
  Files           563      567       +4     
  Lines         15159    15278     +119     
  Branches       1459     1472      +13     
============================================
+ Hits          13644    13759     +115     
- Misses         1044     1048       +4     
  Partials        471      471              

Impacted Files	Coverage Δ
...metry/sdk/testing/assertj/AbstractPointAssert.java	100.00% <ø> (ø)
...etry/sdk/testing/assertj/HistogramPointAssert.java	85.18% <ø> (ø)
...emetry/sdk/testing/assertj/SummaryPointAssert.java	100.00% <ø> (ø)
...lemetry/sdk/testing/assertj/DoubleGaugeAssert.java	100.00% <100.00%> (ø)
...lemetry/sdk/testing/assertj/DoublePointAssert.java	100.00% <100.00%> (ø)
...telemetry/sdk/testing/assertj/DoubleSumAssert.java	100.00% <100.00%> (ø)
...telemetry/sdk/testing/assertj/LongGaugeAssert.java	100.00% <100.00%> (ø)
...telemetry/sdk/testing/assertj/LongPointAssert.java	80.00% <100.00%> (ø)
...entelemetry/sdk/testing/assertj/LongSumAssert.java	100.00% <100.00%> (ø)
...pentelemetry/sdk/testing/assertj/MetricAssert.java	95.23% <100.00%> (ø)
... and 6 more

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[jkwatson]

I'm fine with this change.