docs: Remove 'code-coverage' placeholder directory

In 8 years, this is the first time I see this directory exists
and that there is a Makefile that would write to it.

I don't know if anyone uses that, but PHPUnit auto-creates this
directory as needed. Hence, it need not exist ahead of time.

It seems most contributors generate code coverage by invoking
PHPUnit directory, which requires a path to be specified.

Per https://mediawiki.org/wiki/Manual:PHP_unit_testing/Code_coverage,
this tends to be docs/coverage, not docs/code-coverage.

Change the Makefile to write there as well, as better example,
and also add it to gitignore.

Change-Id: I0a4cf716ea9b7fae89c282945b160b0dc7b2d02f

.gitignore

@@ -25,6 +25,7 @@ sftp-config.json
 
 # MediaWiki install & usage
 /cache
+/docs/coverage
 /docs/js
 /images/[0-9a-f]
 /images/archive

docs/code-coverage/README

@@ -1,2 +0,0 @@
-This directory is for the auto-generated phpunit code coverage.
-Run 'make coverage' in the tests/phpunit subdirectory to build.

tests/phpunit/Makefile

@@ -39,7 +39,7 @@ tap:
 	${PU} --tap
 
 coverage:
-	${PU} --coverage-html ../../docs/code-coverage
+	${PU} --coverage-html ../../docs/coverage
 
 parser:
 	${PU} --group Parser