cmake: delete obsolete TODO items [ci skip]

There is always room for improvement, but CMake is up to par now with
autotools, so there is no longer a good reason to keep around these
inline TODO items.

Answering one of questions:

Q: "The gcc command line use neither -g nor any -O options. As a
   developer, I also treasure our configure scripts's --enable-debug
   option that sets a long range of "picky" compiler options."

A: CMake offers the `CMAKE_BUILD_TYPE` variable to control debug info
   and optimization level. E.g.:
   - `Release`    = `-O3` + no debug info
   - `MinSizeRel` = `-Os` + no debug info
   - `Debug`      = `-O0` + debug info

   https://stackoverflow.com/questions/48754619/what-are-cmake-build-type-debug-release-relwithdebinfo-and-minsizerel/59314670#59314670
   https://cmake.org/cmake/help/latest/manual/cmake-buildsystem.7.html#default-and-custom-configurations

   For picky warnings we have the `PICKY_COMPILER` options, enabled by
   default.

Closes curl#12500

CMakeLists.txt

@@ -26,19 +26,10 @@
 
 # TODO:
 # The output .so file lacks the soname number which we currently have within the lib/Makefile.am file
-# Add full (4 or 5 libs) SSL support
-# Add INSTALL target (EXTRA_DIST variables in Makefile.am may be moved to Makefile.inc so that CMake/CPack is aware of what's to include).
-# Check on all possible platforms
-# Test with as many configurations possible (With or without any option)
-# Create scripts that help keeping the CMake build system up to date (to reduce maintenance). According to Tetetest:
-#  - lists of headers that 'configure' checks for;
-#  - curl-specific tests (the ones that are in m4/curl-*.m4 files);
-#  - (most obvious thing:) curl version numbers.
 # Add documentation subproject
 #
 # To check:
 # (From Daniel Stenberg) The cmake build selected to run gcc with -fPIC on my box while the plain configure script did not.
-# (From Daniel Stenberg) The gcc command line use neither -g nor any -O options. As a developer, I also treasure our configure scripts's --enable-debug option that sets a long range of "picky" compiler options.
 
 # Note: By default this CMake build script detects the version of some
 # dependencies using `check_symbol_exists`.  Those checks do not work