Remove confusing CTest instructions

CTest' defaults suck. On test failure, no output is shown, making it
pointless for developers. Worse, users of 'make test' or 'ninja test'
can't customize the invoked CTest command, and CTest is inconvenient to
call directly (because it requires a `cd` command first).

Drop documentation recommending CTest. Encourage contributors to run the
test executable directly.

docs/BUILDING.md

@@ -8,7 +8,7 @@ Recommended process:
 
 1. Run CMake to create a build directory containing project files.
 2. Run your build tool to compile quick-lint-js and its tests.
-3. Run quick-lint-js' tests directly or using CTest.
+3. Run quick-lint-js' tests directly.
 
 The exact commands you need to run differs depending on your preferred
 development environment and build tool:
@@ -47,11 +47,6 @@ If you only want to build quick-lint-js' tests:
 
 Run the following command to run quick-lint-js' test suite:
 
-    $ ninja -C build test
-
-If you want to run the test executable manually (e.g. to run it with `gdb` or
-`valgrind`):
-
     $ ./build/test/quick-lint-js-test
 
 If you want to run the quick-lint-js program:
@@ -88,11 +83,6 @@ If you only want to build quick-lint-js' tests:
 
 Run the following command to run quick-lint-js' test suite:
 
-    $ make -C build test
-
-If you want to run the test executable manually (e.g. to run it with `gdb` or
-`valgrind`):
-
     $ ./build/test/quick-lint-js-test
 
 If you want to run the quick-lint-js program: