This removes 16k from a release-mode build of the bssl tool. Now that we've
finished the AEAD refactor, there's no use in keeping this around as a
prototype for "stateful AEADs".

Before:
Did 2264000 RC4-MD5 (16 bytes) seal operations in 1000430us (2263026.9 ops/sec): 36.2 MB/s
Did 266000 RC4-MD5 (1350 bytes) seal operations in 1000984us (265738.5 ops/sec): 358.7 MB/s
Did 50000 RC4-MD5 (8192 bytes) seal operations in 1014209us (49299.5 ops/sec): 403.9 MB/s
After:
Did 1895000 RC4-MD5 (16 bytes) seal operations in 1000239us (1894547.2 ops/sec): 30.3 MB/s
Did 199000 RC4-MD5 (1350 bytes) seal operations in 1001361us (198729.5 ops/sec): 268.3 MB/s
Did 39000 RC4-MD5 (8192 bytes) seal operations in 1014832us (38430.0 ops/sec): 314.8 MB/s

There is a non-trivial performance hit, but this cipher doesn't matter much and
the stitched mode code reaches into MD5_CTX and RC4_KEY in somewhat unfortunate
ways.

Change-Id: I9ecd28d6afb54e90ce61baecc641742af2ae6269
Reviewed-on: https://boringssl-review.googlesource.com/6752
Reviewed-by: Adam Langley <agl@google.com>