Do not vendor Brotli libraries

This crate is very outdated. The Brotli version it vendors is old and
affected by CVE-2020-8927. Build against the system-provided libbrotli
instead, that way it can be updated independently, without having to
update the Rust bindings.

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "brotli-sys/brotli"]
-	path = brotli-sys/brotli
-	url = https://github.com/google/brotli

brotli-sys/Cargo.toml

@@ -2,8 +2,6 @@
 name = "brotli-sys"
 version = "0.3.2"
 authors = ["Alex Crichton <[email protected]>"]
-build = "build.rs"
-links = "brotli"
 license = "MIT/Apache-2.0"
 repository = "https://github.com/alexcrichton/brotli2-rs"
 homepage = "https://github.com/alexcrichton/brotli2-rs"
@@ -13,18 +11,5 @@ Raw bindings to libbrotli
 """
 categories = ["external-ffi-bindings"]
 
-include = [
-  "src/*",
-  "brotli/enc/*",
-  "brotli/dec/*",
-  "brotli/common/*",
-  "brotli/include/*",
-  "Cargo.toml",
-  "build.rs"
-]
-
 [dependencies]
 libc = "0.2"
-
-[build-dependencies]
-cc = "1.0"

brotli-sys/src/lib.rs

@@ -57,6 +57,7 @@ pub const BROTLI_DECODER_ERROR_ALLOC_RING_BUFFER_2: BrotliDecoderErrorCode = -27
 pub const BROTLI_DECODER_ERROR_ALLOC_BLOCK_TYPE_TREES: BrotliDecoderErrorCode = -30;
 pub const BROTLI_DECODER_ERROR_UNREACHABLE: BrotliDecoderErrorCode = -31;
 
+#[link(name = "brotlidec")]
 extern "C" {
     pub fn BrotliDecoderCreateInstance(alloc_func: brotli_alloc_func,
                                        free_func: brotli_free_func,
@@ -119,6 +120,7 @@ pub const BROTLI_DEFAULT_MODE: u32 = 0;
 
 pub enum BrotliEncoderState {}
 
+#[link(name = "brotlienc")]
 extern "C" {
     pub fn BrotliEncoderSetParameter(state: *mut BrotliEncoderState,
                                      param: BrotliEncoderParameter,