Drop php-snmp uninstall guidance for SNMPv3 (#232)

Cacti automatically uses the Net-SNMP binaries where php-snmp cannot be
used (SNMPv3 with advanced ciphers, IPv6, bulkwalk, hex output), so users
no longer need to uninstall php-snmp. Reword the SNMP Version 3 note in
Devices.md, soften the optional snmp module note in Requirements.md, and
drop the php-snmp caveat from the SNMP Timeout field in
How-to-Graph-Your-Network.md.

Co-authored-by: TheWitness <copilot@users.noreply.github.com>

Devices.md

@@ -71,10 +71,9 @@ When providing the SNMP credentials, Cacti currently supports the following vers
 
 - **Version 1** - Rarely used any more.  Reserved for very old hardware
 - **Version 2** - Still very popular, and support 64 bit counters except on Windows
-- **Version 3** - Support is provided, but there are presently a limitation.  If you
-  are using advanced settings such as SHA224+ or AES192+ with SNMPv3, you must
-  uninstall the php-snmp module if it's in use in php and leverage the Net-SNMP
-  binaries instead.
+- **Version 3** - Fully supported, including advanced settings such as SHA224+
+  or AES192+ with SNMPv3.  Cacti automatically leverages the Net-SNMP binaries
+  where needed, so there is no need to uninstall the php-snmp module.
 
 When providing the SNMP Credentials, Cacti will warn you if you have provided
 incomplete information depending on the SNMP Version and SNMP Security Level

How-to-Graph-Your-Network.md

@@ -89,7 +89,7 @@ host.
 - **SNMP Port** - UDP port number to use for SNMP (default is 161).
 
 - **SNMP Timeout** - Maximum number of milliseconds Cacti will wait for an SNMP
-  response (does not work with php-snmp support).
+  response.
 
 - **Maximum OID's Per Get Request** - This is a performance feature. Specifies
   the number of OID's that can be obtained in a single SNMP Get request.

Requirements.md

@@ -57,10 +57,10 @@ Cacti requires that the following software is installed on your system.
     - pcntl, posix (Linux only)
 
   - Optional modules:
-    - snmp - The PHP SNMP extension is optional. Cacti selectively bypasses it
-      in favor of Net-SNMP binaries for SNMPv3 queries, IPv6 targets, bulkwalk,
-      and hex-string output. You do not need to remove php-snmp; Cacti handles
-      the fallback automatically based on query type and device configuration.
+    - snmp - The PHP SNMP extension is optional and fully supported. Cacti also
+      uses the Net-SNMP binaries for SNMPv3 queries, IPv6 targets, bulkwalk,
+      and hex-string output. You do not need to remove php-snmp; Cacti selects
+      the right method automatically based on query type and device configuration.
 
 - Problematic software and configuration
   - SELinux, AppArmor, and ModSecurity can interfere with ICMP ping, socket