Back out 4 changesets (bug 777574) because it's the slaves, not the tests

Backed out changeset ce3f48acc244 (bug 777574)
Backed out changeset f3c918a0e91c (bug 777574)
Backed out changeset fd79a8abbbf8 (bug 777574)
Backed out changeset 371e42c987d6 (bug 777574)

--HG--
extra : rebase_source : 04c61c132e85f366088d2318f282acd63b5faa0e

content/canvas/test/webgl/skipped_tests_linux_mesa.txt

@@ -1,8 +1,4 @@
 conformance/limits/gl-max-texture-dimensions.html
 conformance/misc/type-conversion-test.html
-conformance/more/conformance/quickCheckAPI-B2.html
-conformance/more/conformance/quickCheckAPI-B3.html
-conformance/more/conformance/quickCheckAPI-B4.html
-conformance/more/conformance/quickCheckAPI-C.html
 conformance/reading/read-pixels-test.html
 conformance/textures/texture-mips.html