Remove cortex-m-semihosting CI

The current repository CI was copied from cortex-m-semihosting, so it is
not relevant to this one. In the future, it may be worthwhile to add
some proper CI for this repo.

ci/install.sh

@@ -1,12 +0,0 @@
-set -euxo pipefail
-
-main() {
-    if [ $TARGET = thumbv7m-none-eabi ]; then
-        cargo install --list | grep xargo || \
-            cargo install xargo
-        rustup component list | grep 'rust-src.*installed' || \
-            rustup component add rust-src
-    fi
-}
-
-main

ci/script.sh

@@ -1,14 +0,0 @@
-set -euxo pipefail
-
-main() {
-    local cargo=
-    if [ $TARGET = thumbv7m-none-eabi ]; then
-        cargo=xargo
-    else
-        cargo=cargo
-    fi
-
-    $cargo check --target $TARGET
-}
-
-main