remove VoteState::deserialize() from sbf builds

[2501babe]

Problem

the existing VoteState::deserialize implementation overruns the sbf stack and is unusable in a program context. unfortunately, all programs that import solana_program receive a stack size violation warning due to this, regardless of whether they attempt to use the function

compiling spl-token 3.5.0 against solana-program 1.15.3:

   Compiling solana-program v1.15.3 (/home/hana/work/solana/solana/sdk/program)
Error: Function _ZN14solana_program4vote5state9VoteState11deserialize17hbbcc05667760d2caE Stack offset of 6344 exceeded max offset of 4096 by 2248 bytes, please minimize large stack variables
Error: Function _ZN229_$LT$solana_program..vote..state..vote_state_0_23_5.._..$LT$impl$u20$serde..de..Deserialize$u20$for$u20$solana_program..vote..state..vote_state_0_23_5..VoteState0_23_5$GT$..deserialize..__Visitor$u20$as$u20$serde..de..Visitor$GT$9visit_seq17h9e7c929fd7b9125cE Stack offset of 5752 exceeded max offset of 4096 by 1656 bytes, please minimize large stack variables
   Compiling spl-token v3.5.0 (/home/hana/work/solana/spl/token/program)

Summary of Changes

gate the function implementation behind #[cfg(not(target_os = "solana"))]. this breaks no downstream consumers (because the function is not usable as-is) and fixes the warning for everyone

we can handroll a parser for this struct that works in a program context if/when one is required, i just wanted to get this in now that 1.16 exists and 1.15 needs to be stabilized

Fixes #30188

[CriesofCarrots]

Thank you for working on this! lgtm
I vote for v1.15 backport, since this stack-size violation affects all v1.15 program-context users.