Don't log timestamp twice

[singpolyma]

Currently the gem (for example here https://github.com/braintree/braintree_ruby/blob/7d4182b7407bd66061faacadec54960e6c876f72/lib/braintree/http.rb#L138) puts the current time in the log message, however the Logger also put the timestamp at the front of the log, so this is very redundant!

[hollabaq86]

👋 @singpolyma thanks for reaching out, and apologies for the delay! I have a feeling this is a carry over from very early days of Ruby. We'll make a note to fix this up in a future release. Thanks!

[hollabaq86]

for internal tracking, ticket 1904