Remove invalid test runner variation in the UEFI app (#2725)

This config does not behave as intended, as (somewhat counterintuitively) cfg in the config does not have access to all the usual values, including features or in this case test.

See the tracking cargo rust-lang/cargo#8170

experimental/uefi/app/.cargo/config.toml

@@ -1,12 +1,7 @@
 [build]
 target = "x86_64-unknown-uefi"
 
-# Test runners get only one serial port, routed to stdio.
-[target.'cfg(test)']
-runner = "qemu-system-x86_64 -nodefaults -nographic -bios /usr/share/OVMF/OVMF_CODE.fd -serial stdio -machine q35 -device isa-debug-exit,iobase=0xf4,iosize=0x04 -kernel"
-
-# Otherwise, (a) the first serial port gets routed to a log, and (b) the second serial gets attached to stdio.
-[target.'cfg(not(test))']
+[target.x86_64-unknown-uefi]
 runner = "qemu-system-x86_64 -nodefaults -nographic -bios /usr/share/OVMF/OVMF_CODE.fd -serial file:target/console.log -serial stdio -machine q35 -device isa-debug-exit,iobase=0xf4,iosize=0x04 -kernel"
 
 [unstable]