remove unnecessary escaping

[markhermeling]

Fixes #2520 my removing unnecessary escape '' characters.

[lurch]

CI is failing 🙁

CMake Error at cmake/generic_board.cmake:24 (if):
  if given arguments:

RegularExpression::compile(): Unmatched parentheses.
RegularExpression::compile(): Error in compile.
    "LINE" "MATCHES" "^[ 	]*pico_board_cmake_set[ 	]*\\([ 	]*([a-zA-Z_][a-zA-Z0-9_]*)[ 	]*,[ 	]*(.*)[ 	]*)[ 	]*"

  Regular expression "^[ 	]*pico_board_cmake_set[ 	]*\([
  	]*([a-zA-Z_][a-zA-Z0-9_]*)[ 	]*,[ 	]*(.*)[ 	]*)[ 	]*" cannot compile
Call Stack (most recent call first):
  cmake/pico_pre_load_platform.cmake:70 (include)
  pico_sdk_init.cmake:88 (include)
  CMakeLists.txt:8 (include)

[lurch]

I'm afraid it's still failing:

CMake Error at cmake/generic_board.cmake:24 (if):
  if given arguments:

    "LINE" "MATCHES" "^[ 	]*pico_board_cmake_set[ 	]*\\([ 	]*([a-zA-Z_][a-zA-Z0-9_]*)[ 	]*,[ 	]*(.*)[ 	]*)[ 	]*"

  Regular expression "^[ 	]*pico_board_cmake_set[ 	]*\([
  	]*([a-zA-Z_][a-zA-Z0-9_]*)[ 	]*,[ 	]*(.*)[ 	]*)[ 	]*" cannot compile
Call Stack (most recent call first):
  cmake/pico_pre_load_platform.cmake:70 (include)
  pico_sdk_init.cmake:88 (include)
  CMakeLists.txt:8 (include)

[lurch]

CI is now passing, so pinging @will-v-pi

[will-v-pi]

Yes, this looks correct now - the only uneccessary escapes were the \] ones