IpSecManager and IpSecTransform API Cleanup

-Remove Int-based SPI usage from the IpSecTransform.Builder
 This is essentially a less-safe method overload, and it is both
 unnecessary and difficult to implement: the cross-validation
 between SPI and Transform is actually useful, and the kernel
 requires two different mechanisms to use an unreserved vs a
 reserved (alloc'd) SPI: CREATESA vs UPDATESA, which makes this
 hard to support. API Council has questioned the value of this,
 and they are right: everything points to "remove this". In the
 future, if we find that SPI reservation is overhead, we can
 always add it back.

-Hiding the TunnelMode builder method and application/remove
 methods. These will not land by the time the next API
 stabilizes, so better to hide them now that this is a
 near-certainty. Expectation is to un-hide them in the subsequent
 API bump.

Bug: 36073210
Test: Compilation, verified nobody is calling these stubs
Change-Id: Ic1a3f2cf7128633318ac175d6b56b45eb8d21cab