submodules: delete CMSIS_5 from the repository

See https://github.com/raspberrypi/pico-setup/issues/57

Clones of debugprobe or invocations of pico-setup.sh frequently
encounter errors relating to bandwidth budgets. These sporadic errors
are due to the large size of the CMSIS_5 repo clone exhausting the
bandwidth quotas on Github, so drop this in favour of a downstream copy
of the relevant CMSIS-DAP firmware files.

Users are advised to delete and regenerate the build directory.

Optionally, reclaim filesystem space by removing .git/modules/CMSIS_5
and all subdirectories.

.gitmodules

diff --git a/.gitmodules b/.gitmodules
index f8890cf..374afed 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,6 +1,3 @@
-[submodule "CMSIS_5"]
-	path = CMSIS_5
-	url = https://github.com/ARM-software/CMSIS_5
 [submodule "freertos"]
 	path = freertos
 	url = https://github.com/FreeRTOS/FreeRTOS-Kernel

CMSIS_5

diff --git a/CMSIS_5 b/CMSIS_5
deleted file mode 160000
index a65b7c9..0000000
--- a/CMSIS_5
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit a65b7c9a3e6502127fdb80eb288d8cbdf251a6f4