grpc: Revert grpc component name to _grpc

[AbrilRBS]

Summary

Changes to recipe: grpc/[*]

Motivation

The _grpc component might be used in some recipes (See google-cloud-cpp) which breaks when changing the name. For now let's revert it back

Details

#24215 refactored the recipe to make it more maintainable, but this breaking change was not considered important as there was no expectation for the explicit usage of the component outside the recipe

Closes #24698

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• Read the contributing guidelines
• Checked that this PR is not a duplicate: list of PRs by recipe
• Tested locally with at least one configuration using a recent version of Conan

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 3 (65a3003fe45470ae7bc9c354ce421a53a13a6caf):

• grpc/1.65.0:
  All packages built successfully! (All logs)

• grpc/1.54.3:
  All packages built successfully! (All logs)

• grpc/1.50.1:
  All packages built successfully! (All logs)

• grpc/1.50.0:
  All packages built successfully! (All logs)

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Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 3 (65a3003fe45470ae7bc9c354ce421a53a13a6caf):

• grpc/1.65.0:
  All packages built successfully! (All logs)

• grpc/1.54.3:
  All packages built successfully! (All logs)

• grpc/1.50.0:
  All packages built successfully! (All logs)

• grpc/1.50.1:
  All packages built successfully! (All logs)