.NET Core 3.0 is here! (#784)

* .NET Core 3.0 is here!

* Remove IMemoryManager.cs and its references.

* Add T Math/F.FusedMultiplyAdd(T, T, T). Nits.

* Nit.

* Update appveyor.yml

* Revert "Resolve Visual Studio build issues"

This reverts commit 1772128ce0.

* Update SvcTable.cs

Ryujinx/_schema.json

@@ -20,7 +20,6 @@
     "enable_multicore_scheduling",
     "enable_fs_integrity_checks",
     "fs_global_access_log_mode",
-    "enable_legacy_jit",
     "controller_type",
     "enable_keyboard",
     "keyboard_controls",
@@ -472,17 +471,6 @@
         3
       ]
     },
-    "enable_legacy_jit": {
-      "$id": "#/properties/enable_legacy_jit",
-      "type": "boolean",
-      "title": "Enable legacy JIT",
-      "description": "Use old ChocolArm64 ARM emulator",
-      "default": false,
-      "examples": [
-        true,
-        false
-      ]
-    },
     "ignore_missing_services": {
       "$id": "#/properties/ignore_missing_services",
       "type": "boolean",