Use sharded-slab from crates (#4729)

## Problem

We use a patched version of `sharded-slab` with increased MAX_THREADS
[1]. It is not required anymore because safekeepers are async now.

A valid comment from the original PR tho [1]:
> Note that patch can affect other rust services, not only the
safekeeper binary.

- [1] https://github.com/neondatabase/neon/pull/4122

## Summary of changes
- Remove patch for `sharded-slab`

Cargo.lock

@@ -3854,7 +3854,8 @@ dependencies = [
 [[package]]
 name = "sharded-slab"
 version = "0.1.4"
-source = "git+https://github.com/neondatabase/sharded-slab.git?rev=98d16753ab01c61f0a028de44167307a00efea00#98d16753ab01c61f0a028de44167307a00efea00"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "900fba806f70c630b0a382d0d825e17a0f19fcd059a2ade1ff237bcddf446b31"
 dependencies = [
  "lazy_static",
 ]

Cargo.toml

@@ -185,11 +185,6 @@ tonic-build = "0.9"
 # TODO: we should probably fork `tokio-postgres-rustls` instead.
 tokio-postgres = { git = "https://github.com/neondatabase/rust-postgres.git", rev="1aaedab101b23f7612042850d8f2036810fa7c7f" }
 
-# Changes the MAX_THREADS limit from 4096 to 32768.
-# This is a temporary workaround for using tracing from many threads in safekeepers code,
-# until async safekeepers patch is merged to the main.
-sharded-slab = { git = "https://github.com/neondatabase/sharded-slab.git", rev="98d16753ab01c61f0a028de44167307a00efea00" }
-
 ################# Binary contents sections
 
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