Revert the usage of go.opentelemetry.io/proto/slim

[XSAM]

Resolves #5251

Rollback these two PRs:

• otlpmetrichttp: Use go.opentelemetry.io/proto/slim/otlp #5222
• otlploghttp: Use go.opentelemetry.io/proto/slim/otlp #5216

[codecov]

Codecov Report

Attention: Patch coverage is 43.63636% with 217 lines in your changes are missing coverage. Please review.

Project coverage is 84.5%. Comparing base (b34cfc4) to head (5e7e772).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5253     +/-   ##
=======================================
- Coverage   85.5%   84.5%   -1.0%     
=======================================
  Files        258     258             
  Lines      17031   17349    +318     
=======================================
+ Hits       14570   14675    +105     
- Misses      2153    2363    +210     
- Partials     308     311      +3     

Files	Coverage Δ
exporters/otlp/otlplog/otlploghttp/client.go	81.8% <ø> (ø)
...otlp/otlplog/otlploghttp/internal/transform/log.go	95.2% <ø> (ø)
exporters/otlp/otlpmetric/otlpmetrichttp/client.go	82.4% <ø> (ø)
...porters/otlp/otlpmetric/otlpmetrichttp/exporter.go	87.5% <ø> (ø)
...otlpmetric/otlpmetrichttp/internal/otest/client.go	97.7% <ø> (ø)
...ric/otlpmetrichttp/internal/transform/attribute.go	100.0% <ø> (ø)
...pmetric/otlpmetrichttp/internal/transform/error.go	100.0% <ø> (ø)
...ic/otlpmetrichttp/internal/transform/metricdata.go	100.0% <ø> (ø)
...pmetric/otlpmetricgrpc/internal/oconf/envconfig.go	92.9% <95.2%> (+0.9%)	⬆️
...pmetric/otlpmetrichttp/internal/oconf/envconfig.go	92.9% <93.7%> (+0.6%)	⬆️
... and 4 more

[XSAM]

Skip the changelog, as the reverted commits have not been released.