GCHandle leak in OSX Pal SafeDeleteSslContext

[MihaZupan]

We're allocating a weak handle here:

runtime/src/libraries/System.Net.Security/src/System/Net/Security/Pal.OSX/SafeDeleteSslContext.cs

Line 194 in e694e81

GCHandle handle = GCHandle.Alloc(this, GCHandleType.Weak);

But doesn't look like we're ever Free-ing it.

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