1. Runtime flags in CLI Header (documented in § 25.3.3.1) - this byte means in plain words "Is assembly signed?" - if yes, we have a COMIMAGE_FLAGS_STRONGNAMESIGNED value there (8). To remove the strong signing, simply reset this byte back to its current value minus COMIMAGE_FLAGS_STRONGNAMESIGNED. This usually leads to a flag value of COMIMAGE_FLAGS_ILONLY (1).
2. StrongNameSignature RVA in CLI Header (documented in § 25.3.3) - these are 8 bytes, giving an offset of public key hash data. Key is normally 160 (0xA0) bytes itself. To remove strong signing, simply overwrite those 8 bytes in the header with 00. This suggests to the assembly loader that there's no signature in the file, even if the original key is still there.
3. Flags in Assembly Table (documented § 22.2) - this is a 4-byte bitmask of type AssemblyFlags (documented in § 23.1.2). A value of PublicKey (0x0001) here means the assembly is strong signed. To remove strong signing, reset the first byte back to its current value minus PublicKey. This usually resets the flag to SideBySideCompatible value (0x0000).
4. PublicKey index in Assembly Table (documented § 22.2) - this is an index into the Blob heap where the Public Key is stored. To remove strong signing, overwrite those 2 bytes with 00 (meaning, no Public Key available).

MModule mod = new MModule(r);

cliHeaderFlag = mod.ModHeaders.COR20Header.Flags;
cliHeaderFlagOffset = mod.ModHeaders.COR20Header.Start + 16;
strongNameSignatureOffset =
 mod.ModHeaders.COR20Header.StrongNameSignature.Start;
compiledRuntimeVersion =
 mod.ModHeaders.MetaDataHeaders.StorageSigAndHeader.VersionString;
Table tableAssembly = mod.MDTables.GetTable(Types.Assembly);
publicKeyOffset =
 mod.BlobHeap.Start + tableAssembly[0][6].RawData + 1;
assemblyFlag = (uint)tableAssembly[0][5].Data;

// next loop sum tables byte length till
// reaching Assembly Table - this would
// give Assembly Table start offset
long assemblyTableOffset =
     mod.ModHeaders.MetaDataTableHeader.End;
for (int tablesCounter = 0; tablesCounter <
     Int32.Parse(Enum.Format(typeof(Types),
     Types.Assembly, "d")); tablesCounter++)
{
    assemblyTableOffset +=
     mod.MDTables.Tables[tablesCounter].RawData.Length;
}
publicKeyIndexOffset = assemblyTableOffset + 16;
assemblyFlagOffset = assemblyTableOffset + 12;

// next loop sum tables byte length till reaching
// Assembly References Table - this would give
// Assembly References Table start offset
long referenceTableOffset =
     mod.ModHeaders.MetaDataTableHeader.End;
for (int tablesCounter = 0; tablesCounter <
     Int32.Parse(Enum.Format(typeof(Types),
     Types.AssemblyRef, "d")); tablesCounter++)
{
    referenceTableOffset +=
     mod.MDTables.Tables[tablesCounter].RawData.Length;
}