webgl: Enable all the tests on linux

Now that testing is being done using OSMesa on the Linux side as well,
our test behavior matches Mac's pretty closely.

tests/wpt/metadata/webgl/conformance-1.0.3/__dir__.ini

@@ -1,2 +0,0 @@
-disabled:
-  if os == "linux": https://github.com/servo/servo/issues/9331

tests/wpt/metadata/webgl/conformance-1.0.3/conformance/more/functions/readPixelsBadArgs.html.ini

@@ -1,6 +1,8 @@
 [readPixelsBadArgs.html]
   type: testharness
-  expected: TIMEOUT
+  expected:
+    if os == "linux": CRASH
+    if os == "mac": TIMEOUT
   [WebGL test #0: testReadPixels]
     expected: FAIL
 

tests/wpt/metadata/webgl/conformance-1.0.3/conformance/reading/read-pixels-pack-alignment.html.ini

@@ -1,6 +1,8 @@
 [read-pixels-pack-alignment.html]
   type: testharness
-  expected: TIMEOUT
+  expected:
+    if os == "linux": CRASH
+    if os == "mac": TIMEOUT
   [WebGL test #3: successfullyParsed should be true (of type boolean). Was undefined (of type undefined).]
     expected: FAIL
 

tests/wpt/metadata/webgl/conformance-1.0.3/conformance/textures/texture-npot-video.html.ini

@@ -1,5 +1,3 @@
 [texture-npot-video.html]
   type: testharness
-  expected:
-    if os == "linux": CRASH
-    if os == "mac": TIMEOUT
+  expected: TIMEOUT

tests/wpt/metadata/webgl/conformance-1.0.3/conformance/uniforms/uniform-default-values.html.ini

@@ -1,5 +1,3 @@
 [uniform-default-values.html]
   type: testharness
-  expected:
-    if os == "linux": CRASH
-    if os == "mac": ERROR
+  expected: ERROR