Drop the accidentally-tracked-in-working-tree zig-server bench binary
(built by bench/run.sh). Reverted the wasm_check* gitignore entry from
bce53b7 — these are removed, not ignored.
The wasm_check{,2}.{html,js,wasm} files are emscripten smoke-test output
committed by accident in f9ecf9d; nothing in the build/tests/docs
references them. Removed and gitignored the pattern so future WASM
output stays out of the tree.