ARROW-3668: [R} Namespace dependency bit64 is not required

[jameslamb]

The R package is currently broken on Travis because dependency bit64 was recently added but put in Suggests instead of Imports.

In R, every package that you add as an import or importFrom in your NAMESPACE file needs to be in Imports or Depends in DESCRIPTION.

Please consider this PR to address this.

[codecov-io]

Codecov Report

Merging #2888 into master will increase coverage by 1.1%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #2888     +/-   ##
=========================================
+ Coverage   87.33%   88.44%   +1.1%     
=========================================
  Files         417      348     -69     
  Lines       64900    59597   -5303     
=========================================
- Hits        56678    52708   -3970     
+ Misses       8128     6889   -1239     
+ Partials       94        0     -94

Impacted Files	Coverage Δ
rust/src/record_batch.rs
go/arrow/array/table.go
rust/src/array.rs
go/arrow/math/uint64_amd64.go
go/arrow/internal/testing/tools/bool.go
go/arrow/array/bufferbuilder.go
go/arrow/internal/bitutil/bitutil.go
go/arrow/memory/memory_avx2_amd64.go
go/arrow/array/null.go
go/arrow/datatype_nested.go
... and 60 more

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[kszucs]

Actually this is already resolved by #2876

[kszucs]

So I'm closing as a duplicate. However thanks @jameslamb for the fix!

[jameslamb]

Ah sorry, didn't realize! No worries.