[v9] Remove unfitting exports from utils.

[lforst]

Description

Remove everything deprecated in #14267

[AbhiPrasad]

Completed a bunch of these:

• feat(core)!: Remove validSeverityLevels export #14765
• feat(core)!: Remove arrayify method #14782
• feat(core)!: Remove urlEncode method #14783
• feat(core)!: Remove flatten method #14784
• feat(core)!: Remove BAGGAGE_HEADER_NAME export #14785
• feat(core)!: Remove makeFifoCache method #14786

still have TransactionNamingScheme, memoBuilder, and extractRequestData remaining - moving on to some other things but will come back to it when I get time.

[s1gr1d]

Removed TransactionNamingScheme: #14865