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

gm/tests/outputs/nonverbose/output-expected/stdout

Index: gm/tests/outputs/nonverbose/output-expected/stdout
===================================================================
--- gm/tests/outputs/nonverbose/output-expected/stdout	(revision 10989)
+++ gm/tests/outputs/nonverbose/output-expected/stdout	(working copy)
@@ -1,10 +0,0 @@
-GM: These configs will be run: 8888 565
-GM: drawing... selftest1 [300 200]
-GM: Ran 9 tests: NoGpuContext=0 IntentionallySkipped=0 RenderModeMismatch=0 ExpectationsMismatch=0 MissingExpectations=2 WritingReferenceImage=0
-GM: [*] 0 NoGpuContext:
-GM: [ ] 0 IntentionallySkipped
-GM: [*] 0 RenderModeMismatch:
-GM: [*] 0 ExpectationsMismatch:
-GM: [ ] 2 MissingExpectations
-GM: [*] 0 WritingReferenceImage:
-GM: (results marked with [*] will cause nonzero return value)