Removing hsqldb from ext_source since we bootstrap it later

(cherry picked from commit d98be9a24613ebe504de87f0f919d2f1a41bc1d6)

Removing libpng from ext_source, bootstrap it later

(cherry picked from commit 53093d1e6919ddd8041d2ad586cc2c77b5272a27)

Removing icu4c from ext_source since we bootstrap it later

(cherry picked from commit 3ef6d585c1326a9c685cda800b11439a15dffce6)

Removing commons-httpclient from ext_source since we bootstrap it later when needed

(cherry picked from commit 0c352e1497c7f7db4e548ddd1b896c5a24b848e6)

Removing libjpeg from ext_source since we bootstrap and use it later
with a slightly different name.

BTW: The libjpeg bootstrap process really needs to be cleaned up.