Disable solana-metrics dependency for wasm target

[dougEfresh]

Problem

I'm trying to use solana-account-decoder crate in wasm32 target. However, gethostname crate gets pulled in due to dependency on solana-metrics in solana-program-runtime

gethostname v0.2.3
└── solana-metrics v2.1.7
    └── solana-program-runtime v2.1.7
        └── solana-config-program v2.1.7
            └── solana-account-decoder v2.1.7

Summary of Changes

Use build cfg to remove solana-metrics from program-runtime

@ifiokjr FYI

[kevinheavey]

I have a PR open to make metrics optional in program-runtime #3477

[LucasSte]

@dougEfresh I believe @kevinheavey's PR is nicer since it allows anyone to disable metrics. Does it solve your needs as well? I'm learning towards merging that one instead.