Fix VERBOSE make flag (#26289)

The docs say set this to true to enable verbose output, but setting it to
anything, even "false", would enable verbose mode.

The qmk python build program actually does this, supplying "VERBOSE=false"
to make, which turns verbose mode on, not off!  The reason it's not verbose
is that the wrapper also adds the "-s" switch that has the same effect as
turning verbose mode back off.

After fixing the flag, there's no reason to add the "-s", so remove that code.

Makefile

@@ -1,4 +1,4 @@
-ifndef VERBOSE
+ifneq ($(VERBOSE),true)
 .SILENT:
 endif
 

builddefs/build_keyboard.mk

@@ -4,7 +4,7 @@
 # responsible for determining which folder is being used and doing the
 # corresponding environment setup.
 
-ifndef VERBOSE
+ifneq ($(VERBOSE),true)
 .SILENT:
 endif
 

builddefs/build_test.mk

@@ -1,4 +1,4 @@
-ifndef VERBOSE
+ifneq ($(VERBOSE),true)
 .SILENT:
 endif
 

lib/python/qmk/build_targets.py

@@ -113,9 +113,6 @@ class BuildTarget:
             'builddefs/build_keyboard.mk',
         ]
 
-        if not cli.config.general.verbose:
-            compile_args.append('-s')
-
         verbose = 'true' if cli.config.general.verbose else 'false'
         color = 'true' if cli.config.general.color else 'false'