Stored `let` properties of a struct, class, or actor permit
'inout' modification within the constructor body after they have been
initialized. Tentatively remove this rule, only allowing such `let`
properties to be initialized (assigned to) and not treated as `inout`.
Fixes rdar://127258363.
Right now the stdlib/overlays can compile against -Onone tests with or without
-enable-ownership-stripping-after-serialization. This will help me to prevent
other work going on from breaking these properties.
This just eliminates -enable-sil-ownership from all target-swift-frontend and
target-swift-emit-silgen RUN lines. Both of those now include
enable-sil-ownership in their expansion.
*NOTE* DefiniteInit is still running /after/ ownership is stripped. This is just
making sure that the code we are producing can actually pass the verifier.
rdar://31521023
