Revert CROSVM_USE_SYSTEM_* build and CI changes

This setup is no longer needed since:
- The current build system and GPU backend
  integration have been restructured.
- CI now works with the virglrenderer crate.
- Environment variable overrides are no
  longer necessary to avoid CI failures.

Signed-off-by: Dorinda Bassey <[email protected]>

Author: Dorinda Bassey

.buildkite/main-tests.json

@@ -2,7 +2,7 @@
   "tests": [
     {
       "test_name": "build-gnu",
-      "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 RUSTFLAGS=\"-D warnings\" cargo build --release",
+      "command": "RUSTFLAGS=\"-D warnings\" cargo build --release",
       "platform": [
         "x86_64",
         "aarch64",
@@ -27,7 +27,7 @@
     },
     {
       "test_name": "unittests-gnu",
-      "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 cargo test --all-features --workspace",
+      "command": "cargo test --all-features --workspace",
       "platform": [
         "x86_64",
         "aarch64",
@@ -50,7 +50,7 @@
     },
     {
       "test_name": "unittests-gnu-release",
-      "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 cargo test --release --all-features --workspace",
+      "command": "cargo test --release --all-features --workspace",
       "platform": [
         "x86_64",
         "aarch64",
@@ -73,7 +73,7 @@
     },
     {
       "test_name": "clippy",
-      "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 cargo clippy --workspace --bins --examples --benches --all-features --all-targets -- -D warnings -D clippy::undocumented_unsafe_blocks",
+      "command": "cargo clippy --workspace --bins --examples --benches --all-features --all-targets -- -D warnings -D clippy::undocumented_unsafe_blocks",
       "platform": [
         "x86_64",
         "aarch64",
@@ -82,7 +82,7 @@
     },
     {
       "test_name": "check-warnings",
-      "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 RUSTFLAGS=\"-D warnings\" cargo check --all-targets --all-features --workspace",
+      "command": "RUSTFLAGS=\"-D warnings\" cargo check --all-targets --all-features --workspace",
       "platform": [
         "x86_64",
         "aarch64",
@@ -91,7 +91,7 @@
     },
     {
       "test_name": "coverage",
-      "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 pytest $(find . -type f -name \"test_coverage.py\")",
+      "command": "pytest $(find . -type f -name \"test_coverage.py\")",
       "docker_plugin": {
         "privileged": true
       },

vhost-device-gpu/README.md

@@ -90,23 +90,10 @@ Because blob resources are not yet supported, some capsets are limited:
 The device leverages the [rutabaga_gfx](https://crates.io/crates/rutabaga_gfx)
 crate to provide rendering with virglrenderer and gfxstream.
 
-This crate supports two GPU backends: gfxstream (default) and virglrenderer.
-Both require the system-provided virglrenderer and minigbm libraries due to the dependence on rutabaga_gfx.
-
-Install the development packages for your distro, then build with:
-
-```session
-CROSVM_USE_SYSTEM_VIRGLRENDERER=1 \
-CROSVM_USE_SYSTEM_MINIGBM=1 \
-cargo build
-```
-
 gfxstream support is compiled by default, it can be disabled by not building with the `gfxstream` feature flag, for example:
 
 ```session
-CROSVM_USE_SYSTEM_VIRGLRENDERER=1 \
-CROSVM_USE_SYSTEM_MINIGBM=1 \
-cargo build --no-default-features
+$ cargo build --no-default-features
 ```
 
 With Virglrenderer, Rutabaga translates OpenGL API and Vulkan calls to an