Remove lambda attributes

[coltonweaver]

Issue #, if available:

N/A

Description of changes:

This PR removes the #[lambda] macro from this library. @davidbarsky provided the following valid reasons for why this should be done:

• Compiler error reporting is not handled correctly using this macro, so the spans where an error occurs are undefined and point to incorrect locations.
• Using this macro conflates warm and cold starts for Lambda functions, as this removes the ability to initialize global resources that might panic if initialized twice, such as a global logger.

Given that the alternative to using this macro is a single line addition to a main function, there is no real need to continue supporting this macro.

By submitting this pull request

• [*] I confirm that my contribution is made under the terms of the Apache 2.0 license.
• [*] I confirm that I've made a best effort attempt to update all relevant documentation.

[bahildebrand]

LGTM