Remove --cfg uuid_unstable requirement for uuid_v7 feature

[SanchithHegde]

Issue #, if available:

Description of changes:

This PR removes the requirement that RUSTFLAGS="--cfg uuid_unstable" be provided to use the uuid_v7 feature flag, and thus the v7 feature flag from the uuid crate.

The uuid crate stabilized support for UUID v6-v8 in uuid-rs/uuid#718, which was included in the 1.6.0 release of the uuid crate. Since tracing-actix-web pulls the uuid crate using only the major version (1) and does not include the minor version, I believe it is safe to remove the --cfg uuid_unstable requirement.

Essentially, I just went through the changes done in #116 and removed some lines which were no longer applicable.

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[LukeMathWalker]

That works, thanks!