ARROW-12224: [Rust] Use stable rust for no default test, clean up CI tests

[alamb]

Rationale

1. As @jorgecarleitao noted on ARROW-12204: [Rust][CI] Reduce size of Rust build artifacts in integration test #9889 (comment), we should be running the check if arrow compiles with stable rust as that is what we target for the arrow crate
2. I noticed that there were several redundant (and inconsistent) settings of RUSTFLAGS
3. The titles of many of the tests are confusing (to me) as they have a lot of detailed architecture / rust version information before the description of what they are testing

Changes

1. Use rust stable for the check that ensures the crate builds without default features
2. Remove redundant RUSTFLAGS
3. Change titles of the jobs to consistently start with a description of what they do

Note

This could be three individual PRs, but I wanted to avoid the overhead of three separate JIRA tickets and juggling several concurrent potentially conflicting PRs. I will break it into three individual ones however if reviewers want.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-12224

[codecov-io]

Codecov Report

Merging #9904 (dad8209) into master (dd8cd10) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #9904   +/-   ##
=======================================
  Coverage   82.71%   82.71%           
=======================================
  Files         256      256           
  Lines       60186    60186           
=======================================
  Hits        49780    49780           
  Misses      10406    10406           

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[jorgecarleitao]

LGTM Thanks a lot!

[jorgecarleitao]

@kszucs has raised in the past the he would prefer to have the same names as other implementations.

pinging him here.

[alamb]

Thanks for the hint @jorgecarleitao -- will wait for @kszucs to weigh in

[kszucs]

I prefer this convention to remain consistent with the rest of the workflows (C++, Python, Ruby, etc.).
I'm fine with using a different naming convention too if you think that helps distinguishing the builds.

[alamb]

I think it will help. Let's try this way and see how we like it. Thanks @kszucs 👍