Allow proc-macro2 dependency to be flexible in arrow-flight

[alamb]

Which issue does this PR close?

Resolves #1101

Rationale for this change

Hard pinning the version means fixes that require updates to the proc-macro2 library are not possible

Specifically this also fixes this breakage with thequote 1.11.0 release

cd /Users/alamb/Software/arrow-rs && CARGO_TARGET_DIR=/Users/alamb/Software/df-target cargo test --all
    Updating crates.io index
   Compiling quote v1.0.11
error[E0599]: no function or associated item named `from_str_unchecked` found for struct `proc_macro2::Literal` in the current scope
   --> /Users/alamb/.cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/quote-1.0.11/src/runtime.rs:301:41
    |
301 |         let literal = unsafe { Literal::from_str_unchecked(repr) };
    |                                         ^^^^^^^^^^^^^^^^^^ function or associated item not found in `proc_macro2::Literal`

error[E0599]: no function or associated item named `from_str_unchecked` found for struct `proc_macro2::Literal` in the current scope
   --> /Users/alamb/.cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/quote-1.0.11/src/runtime.rs:310:45
    |
310 |         let mut literal = unsafe { Literal::from_str_unchecked(repr) };
    |                                             ^^^^^^^^^^^^^^^^^^ function or associated item not found in `proc_macro2::Literal`

For more information about this error, try `rustc --explain E0599`.
error: could not compile `quote` due to 2 previous errors

What changes are included in this PR?

Make pin to proc-macro2 more flexble

Are there any user-facing changes?

[liukun4515]

Thanks,
LGTM

[alamb]

I will prepare a backport of this to active_release in case we can't get @dtolnay to yank the offending quote 1.0.11 release from crates.io