Remove or change default for `BILBY_INCLUDE_GLOBAL_META_DATA` in 3.0

[mj-will]

#915 introduced the environment variable BILBY_INCLUDE_GLOBAL_META_DATA which is false default. This ensured that results where backwards compatible and didn't break PESummary at the time.

I propose we either change the default to True or remove it entirely in bilby 3.0. Thoughts?