Remove time check in connection pool spec

There isn't any sleeps involved here to check for concurrent vs
sequential operation, so there is no reason to check for time
elapsed.  I've seen this spec fail for old Ruby versions during
high concurrent load (parallel testing) due to this, and it seems
best to remove the check.

spec/core/connection_pool_spec.rb

@@ -365,7 +365,6 @@ def pool._acquire(*)
  @pool.disconnect
  b = @icpp
 
- time = Time.now
  cc = {}
  threads = []
  results = []
@@ -387,7 +386,6 @@ def pool._acquire(*)
  5.times{|i| q.pop}
  results.sort.must_equal (1..5).to_a
  threads.each(&:join)
- (Time.now - time).must_be :<, 0.75
 
  threads.each{|t| t.wont_be :alive?}
  cc.size.must_equal 5