EDIT: I misunderstood the question, original answer below
Standard HTTPS will protect everything from evesdroppers on the network; the POST data, any HTTP headers, cookies, even the URL that they are accessing.
If your site has standard HTTPS, then you do not need extra encryption of the content. Yes, you can remove that extra call to
Even if you're encrypting the content of your POST bodies, what about the rest of the HTTP message?
Here's a sample GET for loading this page (all cookie values changed to X)
GET /questions/224647/unnecessary-ssl-encryption-in-api HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:72.0) Gecko/20100101 Firefox/72.0
Accept-Encoding: gzip, deflate
__utmt=1; _ga=GA1.X; _gid=GA1.X
If the HTTP headers on your API include sensitive information like the user's IP address, user agent, auth token, cookies, even which URL they are accessing is sometimes considered sensitive, then you need TLS / SSL to encrypt that.