gm self-tests: stop comparing stdout/stderr/command_line, just look at JSON summary

gm/tests/outputs/compared-against-identical-bytes-json/output-expected/stdout

Index: gm/tests/outputs/compared-against-identical-bytes-json/output-expected/stdout
===================================================================
--- gm/tests/outputs/compared-against-identical-bytes-json/output-expected/stdout	(revision 10989)
+++ gm/tests/outputs/compared-against-identical-bytes-json/output-expected/stdout	(working copy)
@@ -1,18 +0,0 @@
-GM: These configs will be run: 8888 565
-GM: reading expectations from JSON summary file gm/tests/inputs/json/identical-bytes.json
-GM: writing to gm/tests/outputs/compared-against-identical-bytes-json/output-actual/writePath
-GM: writing mismatches to gm/tests/outputs/compared-against-identical-bytes-json/output-actual/mismatchPath
-GM: writing images without expectations to gm/tests/outputs/compared-against-identical-bytes-json/output-actual/missingExpectationsPath
-GM: drawing... selftest1 [300 200]
-GM: Ran 1 GMs
-GM: ... over  2 configs ["8888", "565"]
-GM: ...  and  7 modes   ["pipe", "pipe cross-process", "pipe cross-process, shared address", "replay", "rtree", "serialize", "tilegrid"]
-GM: ... so there should be a total of 9 tests.
-GM: Ran 9 tests: NoGpuContext=0 IntentionallySkipped=0 RenderModeMismatch=0 ExpectationsMismatch=0 MissingExpectations=0 WritingReferenceImage=0
-GM: [*] 0 NoGpuContext:
-GM: [ ] 0 IntentionallySkipped:
-GM: [*] 0 RenderModeMismatch:
-GM: [*] 0 ExpectationsMismatch:
-GM: [ ] 0 MissingExpectations:
-GM: [*] 0 WritingReferenceImage:
-GM: (results marked with [*] will cause nonzero return value)