remove redundant into_iter() calls

[jimexist]

Which issue does this PR close?

Closes #.

Rationale for this change

remove redundant into_iter calls because Vec<Result<_>> can automatically be transposed to Result<Vec<_>> - there is no need for additional into_iter calls

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #527 (7792c6c) into master (d5bca0e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #527   +/-   ##
=======================================
  Coverage   76.03%   76.03%           
=======================================
  Files         157      157           
  Lines       26990    26990           
=======================================
  Hits        20521    20521           
  Misses       6469     6469           

Impacted Files	Coverage Δ
...sta/rust/core/src/serde/logical_plan/from_proto.rs	35.20% <ø> (ø)
datafusion/src/physical_plan/windows.rs	86.22% <ø> (ø)
datafusion/src/sql/planner.rs	84.62% <ø> (ø)

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[alamb]

I am surprised Clippy didn't complain about this ;)