rpc/stream/vc/writer: Remove defer statement.
rpc/stream/vc/writer: Remove defer statement.

Found another one in writer.

v23 go test -bench=Benchmark_100KB -cpu=1 -benchtime=20s v.io/x/ref/runtime/internal/rpc/benchmark

Benchmark_100KB    10000     2299916 ns/op    86.96 MB/s
--- Histogram (unit: ms)
  Count: 10000  Min: 1  Max: 9  Avg: 1.62
  ------------------------------------------------------------
  [  1,   2)   5927   59.3%   59.3%  ######
  [  2,   3)   2085   20.9%   80.1%  ##
  [  3,   4)   1924   19.2%   99.4%  ##
  [  4,   5)     22    0.2%   99.6%
  [  5,   6)     39    0.4%  100.0%
  [  6,   8)      1    0.0%  100.0%
  [  8,  10)      2    0.0%  100.0%
  [ 10,  12)      0    0.0%  100.0%
  [ 12, inf)      0    0.0%  100.0%
ok    v.io/x/ref/runtime/internal/rpc/benchmark 23.626s

Benchmark_100KB    10000     2240760 ns/op    89.26 MB/s
--- Histogram (unit: ms)
  Count: 10000  Min: 1  Max: 5  Avg: 1.56
  ------------------------------------------------------------
  [  1,   2)   6190   61.9%   61.9%  ######
  [  2,   3)   1989   19.9%   81.8%  ##
  [  3,   4)   1809   18.1%   99.9%  ##
  [  4,   5)     10    0.1%  100.0%
  [  5, inf)      2    0.0%  100.0%
ok    v.io/x/ref/runtime/internal/rpc/benchmark 23.115s

Change-Id: I82f96a681de8375372eab25bba9bae94ca17e020

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref