gcc wrappers still don't actually work, remove them

[DanAlbert]

From my comments here: https://stackoverflow.com/a/53535894/632035

The fake GCC wrappers we have that point to Clang can find the linker now, but still won't find the CRT objects since Clang will only search the sysroot for them, and can't do that properly without a versioned target. GCC would search -L directories.

The goal of these was to keep old build scripts working without changes to the command line. Given that a future release (r21? gradle changes haven't landed yet so maybe further out) will remove the $NDK/platforms directory and whatnot to save space, which will break all these use cases anyway. Given that, and that it would probably take a Clang change that we don't actually want to get the wrappers working, we should probably just remove them.

Alternatively, we could have the GCC wrappers select an Android release by default. The user's -L would override so it would get the right libraries, but it would get the wrong CRT objects. I don't think we should do this, but I don't see other ways of getting these working short of undesirable Clang changes (which would have a long enough lead time that they're probably pointless anyway).