Refactoring of core security to remove the factories.

- Renamed security_context -> security_connector.
- Credentials are now responsible for creating their own connectors.
diff --git a/build.json b/build.json
index 58837e2..e74fa64 100644
--- a/build.json
+++ b/build.json
@@ -386,7 +386,7 @@
       "headers": [
         "src/core/httpcli/format_request.h",
         "src/core/httpcli/httpcli.h",
-        "src/core/httpcli/httpcli_security_context.h",
+        "src/core/httpcli/httpcli_security_connector.h",
         "src/core/httpcli/parser.h",
         "src/core/security/auth.h",
         "src/core/security/base64.h",
@@ -394,7 +394,7 @@
         "src/core/security/json_token.h",
         "src/core/security/secure_endpoint.h",
         "src/core/security/secure_transport_setup.h",
-        "src/core/security/security_context.h",
+        "src/core/security/security_connector.h",
         "src/core/tsi/fake_transport_security.h",
         "src/core/tsi/ssl_transport_security.h",
         "src/core/tsi/transport_security.h",
@@ -403,19 +403,18 @@
       "src": [
         "src/core/httpcli/format_request.c",
         "src/core/httpcli/httpcli.c",
-        "src/core/httpcli/httpcli_security_context.c",
+        "src/core/httpcli/httpcli_security_connector.c",
         "src/core/httpcli/parser.c",
         "src/core/security/auth.c",
         "src/core/security/base64.c",
         "src/core/security/credentials.c",
         "src/core/security/credentials_posix.c",
         "src/core/security/credentials_win32.c",
-        "src/core/security/factories.c",
         "src/core/security/google_default_credentials.c",
         "src/core/security/json_token.c",
         "src/core/security/secure_endpoint.c",
         "src/core/security/secure_transport_setup.c",
-        "src/core/security/security_context.c",
+        "src/core/security/security_connector.c",
         "src/core/security/server_secure_chttp2.c",
         "src/core/surface/init_secure.c",
         "src/core/surface/secure_channel_create.c",