Revert "Limit the maximum memory on AppVeyor since we have 4 processe…

…s now."

This reverts commit 6acfe2b.

AppVeyor went back to 2 cores. The restarting of workers makes it harder to
see what's going on in one of the timeout failure modes we see on appveyor,
where one of the workers gets stuck in an early test.

appveyor.yml

@@ -3,7 +3,6 @@ environment:
   matrix:
   - ARCH: "i686"
   - ARCH: "x86_64"
-    JULIA_TEST_MAXRSS_MB: 480
 
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