ci: drop all custom tests

They were all related to testing specific features, but since the CI by
default now uses cargo-all-features, this is redundant.

Leave custom-tests.json around, as removing it would mean we also have
to modify the buildkite pipeline definition itself, and that's always a
bit messy to coordinate with the merging of PRs.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

.buildkite/custom-tests.json

@@ -1,38 +1,3 @@
 {
-    "tests": [
-        {
-            "test_name": "build-fam-gnu",
-            "command": "cargo build --release --features=fam-wrappers",
-            "platform": [
-                "x86_64",
-                "aarch64",
-                "riscv64"
-            ]
-        },
-        {
-            "test_name": "build-fam-musl",
-            "command": "cargo build --release --features=fam-wrappers --target {target_platform}-unknown-linux-musl",
-            "platform": [
-                "x86_64",
-                "aarch64"
-            ]
-        },
-        {
-            "test_name": "build-serde-gnu",
-            "command": "cargo build --release --features=serde",
-            "platform": [
-                "x86_64",
-                "aarch64",
-                "riscv64"
-            ]
-        },
-        {
-            "test_name": "build-serde-musl",
-            "command": "cargo build --release --features=serde --target {target_platform}-unknown-linux-musl",
-            "platform": [
-                "x86_64",
-                "aarch64"
-            ]
-        }
-    ]
+    "tests": []
 }