Remove recipe for RocksDB and add recipe for Snappy (#4431)

- Copies the recipe for Snappy from Conan Center, but removes three
  lines that explicitly link the standard library, which prevents
  builders from statically linking it.
- Removes the recipe for RocksDB now that an official recipe for version
  6.27.3 is in Conan Center.

Developers will likely need to remove cached versions of both RocksDB
and Snappy:

```
conan remove -f rocksdb
conan remove -f snappy
```

---------

Co-authored-by: John Freeman <jfreeman08@gmail.com>

external/snappy/conanfile.py

@@ -0,0 +1,89 @@
+from conan import ConanFile
+from conan.tools.build import check_min_cppstd
+from conan.tools.cmake import CMake, CMakeToolchain, cmake_layout
+from conan.tools.files import apply_conandata_patches, copy, export_conandata_patches, get, rmdir
+from conan.tools.scm import Version
+import os
+
+required_conan_version = ">=1.54.0"
+
+
+class SnappyConan(ConanFile):
+    name = "snappy"
+    description = "A fast compressor/decompressor"
+    topics = ("google", "compressor", "decompressor")
+    url = "https://github.com/conan-io/conan-center-index"
+    homepage = "https://github.com/google/snappy"
+    license = "BSD-3-Clause"
+
+    package_type = "library"
+    settings = "os", "arch", "compiler", "build_type"
+    options = {
+        "shared": [True, False],
+        "fPIC": [True, False],
+    }
+    default_options = {
+        "shared": False,
+        "fPIC": True,
+    }
+
+    def export_sources(self):
+        export_conandata_patches(self)
+
+    def config_options(self):
+        if self.settings.os == 'Windows':
+            del self.options.fPIC
+
+    def configure(self):
+        if self.options.shared:
+            self.options.rm_safe("fPIC")
+
+    def layout(self):
+        cmake_layout(self, src_folder="src")
+
+    def validate(self):
+        if self.settings.compiler.get_safe("cppstd"):
+            check_min_cppstd(self, 11)
+
+    def source(self):
+        get(self, **self.conan_data["sources"][self.version], strip_root=True)
+
+    def generate(self):
+        tc = CMakeToolchain(self)
+        tc.variables["SNAPPY_BUILD_TESTS"] = False
+        if Version(self.version) >= "1.1.8":
+            tc.variables["SNAPPY_FUZZING_BUILD"] = False
+            tc.variables["SNAPPY_REQUIRE_AVX"] = False
+            tc.variables["SNAPPY_REQUIRE_AVX2"] = False
+            tc.variables["SNAPPY_INSTALL"] = True
+        if Version(self.version) >= "1.1.9":
+            tc.variables["SNAPPY_BUILD_BENCHMARKS"] = False
+        tc.generate()
+
+    def build(self):
+        apply_conandata_patches(self)
+        cmake = CMake(self)
+        cmake.configure()
+        cmake.build()
+
+    def package(self):
+        copy(self, "COPYING", src=self.source_folder, dst=os.path.join(self.package_folder, "licenses"))
+        cmake = CMake(self)
+        cmake.install()
+        rmdir(self, os.path.join(self.package_folder, "lib", "cmake"))
+
+    def package_info(self):
+        self.cpp_info.set_property("cmake_file_name", "Snappy")
+        self.cpp_info.set_property("cmake_target_name", "Snappy::snappy")
+        # TODO: back to global scope in conan v2 once cmake_find_package* generators removed
+        self.cpp_info.components["snappylib"].libs = ["snappy"]
+        if not self.options.shared:
+            if self.settings.os in ["Linux", "FreeBSD"]:
+                self.cpp_info.components["snappylib"].system_libs.append("m")
+
+        # TODO: to remove in conan v2 once cmake_find_package* generators removed
+        self.cpp_info.names["cmake_find_package"] = "Snappy"
+        self.cpp_info.names["cmake_find_package_multi"] = "Snappy"
+        self.cpp_info.components["snappylib"].names["cmake_find_package"] = "snappy"
+        self.cpp_info.components["snappylib"].names["cmake_find_package_multi"] = "snappy"
+        self.cpp_info.components["snappylib"].set_property("cmake_target_name", "Snappy::snappy")