[2019-02] [System.Core] Ensure monotouch[_runtime] API are identical (#14616)
* [System.Core] Ensure monotouch[_runtime] API are identical
Ensure the API surface for `System.Core.dll` is identical between the
`monotouch` and `monotouch_runtime` (used for REPL and the interpreter).
This ensure code compiled against one will be fine when building against
the other (e.g. avoiding linker errors).
Removed methods:
```csharp
public void CompileToMethod (System.Reflection.Emit.MethodBuilder method);
public void CompileToMethod (System.Reflection.Emit.MethodBuilder method, System.Runtime.CompilerServices.DebugInfoGenerator debugInfoGenerator);
```
Removed methods:
```csharp
[Obsolete ("do not use this method")]
public static IRuntimeVariables MergeRuntimeVariables (IRuntimeVariables first, IRuntimeVariables second, int[] indexes);
[Obsolete ("do not use this method")]
public static System.Linq.Expressions.Expression Quote (System.Linq.Expressions.Expression expression, object hoistedLocals, object[] locals);
```
* [csproj] Update project files
* Bump API snapshot submodule
* [csproj] Update project files