boards: cc26x2r1_launchxl: remove unnecessary openocd workaround

The workaround doesn't seem to be necessary when using latest XDS110
firmware (3.0.0.13).

Signed-off-by: Gerard Marull-Paretas <[email protected]>

Author: gmarull

boards/arm/cc26x2r1_launchxl/support/openocd.cfg

@@ -1,4 +1 @@
 source [find board/ti_cc26x2_launchpad.cfg]
-# Workaround for #21372. This allows OpenOCD to flash correctly
-# with newer 3.x XDS firmware
-adapter_khz 1500