[infra] Change language attribute from "cpp" to "c++" in build scripts. (#3493)

* [infra] Change language attribute from "cpp" to "c++" in coverage job runner.

Should've done this in https://github.com/google/oss-fuzz/pull/3477. Good news is that nothing failed, the coverage job was just skipped for pretty much all projects.

* also remove default value from build_project script

infra/gcb/build_and_run_coverage.py

@@ -36,7 +36,7 @@ LATEST_REPORT_INFO_CONTENT_TYPE = 'application/json'
 UPLOAD_URL_FORMAT = 'gs://' + COVERAGE_BUCKET_NAME + '/{project}/{type}/{date}'
 
 # Languages from project.yaml that have code coverage support.
-LANGUAGES_WITH_COVERAGE_SUPPORT = ['c', 'cpp']
+LANGUAGES_WITH_COVERAGE_SUPPORT = ['c', 'c++']
 
 
 def skip_build(message):

infra/gcb/build_project.py

@@ -61,7 +61,6 @@ def load_project_yaml(project_dir):
     project_yaml.setdefault('run_tests', True)
     project_yaml.setdefault('coverage_extra_args', '')
     project_yaml.setdefault('labels', {})
-    project_yaml.setdefault('language', 'cpp')
     return project_yaml