Drop HRSS assembly.

While this assembly implementation is faster in microbenchmarks, the
cache pressure makes it slightly worse than the C code in larger
benchmarks.

Before:

Did 7686 HRSS generate operations in 1056025us (7278.2 ops/sec)
Did 90000 HRSS encap operations in 1010095us (89100.5 ops/sec)
Did 28000 HRSS decap operations in 1031008us (27157.9 ops/sec)

After:

Did 3523 HRSS generate operations in 1045508us (3369.7 ops/sec)
Did 43000 HRSS encap operations in 1017077us (42278.0 ops/sec)
Did 17000 HRSS decap operations in 1011170us (16812.2 ops/sec)

Change-Id: Ia7745b50393f2d2849867e7c5c0af59d651f243d
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55885
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>

crypto/CMakeLists.txt

@@ -149,7 +149,6 @@ if(ARCH STREQUAL "x86_64")
     chacha/chacha-x86_64.${ASM_EXT}
     cipher_extra/aes128gcmsiv-x86_64.${ASM_EXT}
     cipher_extra/chacha20_poly1305_x86_64.${ASM_EXT}
-    hrss/asm/poly_rq_mul.S
     test/trampoline-x86_64.${ASM_EXT}
   )
 endif()