Do not collect compile-time metrics for T21839r

...the testsuite doesn't handle this properly since it
also collects run-time metrics.  Compile-time metrics
for this test are already tracked via T21839c.

Metric Decrease:
    T21839r

testsuite/tests/perf/compiler/T21839c.stdout

-10008

testsuite/tests/perf/compiler/all.T

@@ -646,6 +646,9 @@ test ('T20261',
       [''])
 
 # Track perf of generics based binary instances
+# See also T21839r in perf/should_run... the testsuite
+# does not sensibly handle one test acting as both
+# a compile-time and a run-time performance test
 test('T21839c',
     [   collect_compiler_stats('all', 10),
         collect_compiler_stats('bytes allocated', 1),

testsuite/tests/perf/should_run/all.T

@@ -400,11 +400,13 @@ test('T19347',
     compile_and_run,
     ['-O'])
 
-# Track perf of generics based binary instances
+# Track runtime perf of generics based binary instances
+# See also T21839c in perf/compiler... the testsuite
+# does not sensibly handle one test acting as both
+# a compile-time and a run-time performance test
 test('T21839r',
     [   collect_stats('bytes allocated', 10),
         collect_runtime_residency(10),
-        collect_compiler_stats('bytes allocated', 1),
         only_ways(['normal'])],
     compile_and_run,
     ['-O'])