Fix trivial nits in documentaion

Code Health (Tuesday?): Parameters' names are not correct.
Reviewed-by: NBen Kaduk <kaduk@mit.edu>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4117)

doc/man3/EVP_DigestSignInit.pod

@@ -23,7 +23,7 @@ EVP_DigestSign - EVP signing functions
 The EVP signature routines are a high level interface to digital signatures.
 
 EVP_DigestSignInit() sets up signing context B<ctx> to use digest B<type> from
-ENGINE B<impl> and private key B<pkey>. B<ctx> must be created with
+ENGINE B<e> and private key B<pkey>. B<ctx> must be created with
 EVP_MD_CTX_new() before calling this function. If B<pctx> is not NULL the
 EVP_PKEY_CTX of the signing operation will be written to B<*pctx>: this can
 be used to set alternative signing options.

doc/man3/EVP_DigestVerifyInit.pod

@@ -22,7 +22,7 @@ EVP_DigestVerify - EVP signature verification functions
 The EVP signature routines are a high level interface to digital signatures.
 
 EVP_DigestVerifyInit() sets up verification context B<ctx> to use digest
-B<type> from ENGINE B<impl> and public key B<pkey>. B<ctx> must be created
+B<type> from ENGINE B<e> and public key B<pkey>. B<ctx> must be created
 with EVP_MD_CTX_new() before calling this function. If B<pctx> is not NULL the
 EVP_PKEY_CTX of the verification operation will be written to B<*pctx>: this
 can be used to set alternative verification options.