Remove serialize feature

[jtescher]

Removes non-spec serialization support to reduce public API surface area.

[codecov]

Codecov Report

Merging #738 (31ca9ed) into main (e108b1e) will decrease coverage by 21.92%.
The diff coverage is 25.78%.

@@             Coverage Diff             @@
##             main     #738       +/-   ##
===========================================
- Coverage   71.54%   49.61%   -21.93%     
===========================================
  Files         102      103        +1     
  Lines        8611     6973     -1638     
===========================================
- Hits         6161     3460     -2701     
- Misses       2450     3513     +1063     

Impacted Files	Coverage Δ
opentelemetry-api/src/attributes/encoder.rs	0.00% <ø> (ø)
opentelemetry-api/src/attributes/mod.rs	41.93% <ø> (ø)
opentelemetry-api/src/baggage.rs	0.00% <ø> (ø)
opentelemetry-api/src/context.rs	33.00% <0.00%> (ø)
opentelemetry-api/src/global/error_handler.rs	0.00% <ø> (ø)
opentelemetry-api/src/global/metrics.rs	83.33% <ø> (ø)
opentelemetry-api/src/global/trace.rs	30.00% <ø> (ø)
opentelemetry-api/src/metrics/async_instrument.rs	0.00% <ø> (ø)
opentelemetry-api/src/metrics/config.rs	50.00% <ø> (ø)
opentelemetry-api/src/metrics/descriptor.rs	71.69% <ø> (ø)
... and 110 more

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